Pressure-sensitive adhesive tape and tape roll

ABSTRACT

A pressure-sensitive adhesive tape includes: a pressure-sensitive adhesive layer that contains at least a fine particle and/or a bubble and both the surfaces of which are pressure-sensitive adhesive surfaces; and a release liner having both a first release layer that is provided on one surface of the pressure-sensitive adhesive layer so as to contact the one surface and a second release layer located opposite to the first release layer. The thickness of the pressure-sensitive adhesive layer is 0.2 to 2.0 mm. The second release layer of the release liner is structured such that a holding time measured by a predetermined method is 2500 minutes or longer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior International Patent Application No. PCT/JP 2012/002353, filedon Apr. 4, 2012, the entire content of each of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pressure-sensitive adhesive tape. Theinvention particularly relates to a tape roll (double-sidedpressure-sensitive adhesive tape wound body) in which apressure-sensitive adhesive layer, both the surfaces of which arepressure-sensitive adhesive surfaces, and a release liner laminated onthe pressure-sensitive adhesive layer are wound into a roll shape.

2. Description of the Related Art

From the past, double-sided pressure-sensitive adhesive tapes, both thesurfaces of which are pressure-sensitive adhesive surfaces, are widelyused as means for joining members together. In particular, acrylicdouble-sided pressure-sensitive adhesive tapes, each having an acrylicpressure-sensitive adhesive layer as the pressure-sensitive adhesivelayer, are excellent: in light resistance, weatherability, and oilresistance, etc.; in pressure-sensitive adhesive properties such aspressure-sensitive adhesive force and cohesive force; and in anti-agingproperties such as heat resistance and weatherability, and hence theyare widely used. The applications of the acrylic pressure-sensitiveadhesive tapes particularly include an application to adherends havinglow polarity, such as polystyrene, ABS, and polycarbonate, which arewidely used as materials for home electronic appliances and buildingmaterials, etc.

When a pressure-sensitive adhesive tape is stored in the state of beingwound into a roll shape, part of a pressure-sensitive adhesive mayprotrude from a side portion of the roll, depending on storageconditions or storage states. There is the problem that such aphenomenon becomes remarkable when, in a double-sided pressure-sensitiveadhesive tape wound body in which a pressure-sensitive adhesive layer,both the surfaces of which are pressure-sensitive adhesive surfaces, anda release liner laminated on the pressure-sensitive adhesive layer arewound into a roll shape, the thickness of the pressure-sensitiveadhesive layer is made large or fine particles and/or bubbles arecontained in the pressure-sensitive adhesive layer in order to improveadhesive performance.

The present invention has been made in view of these situations, and apurpose of the invention is to provide a technique in which oozing of apressure-sensitive adhesive from a pressure-sensitive adhesive tapewound into a roll shape is suppressed.

SUMMARY OF THE INVENTION

An aspect of the present invention is a pressure-sensitive adhesivetape. The pressure-sensitive adhesive tape includes: apressure-sensitive adhesive layer that contains at least a fine particleand/or a bubble and both the surfaces of which are pressure-sensitiveadhesive surfaces; and a release liner having both a release layer (a)that is provided on one surface (1) of the pressure-sensitive adhesivelayer so as to contact the one surface (1) and a back surface releaselayer (b) located opposite to the release layer (a). The thickness ofthe pressure-sensitive adhesive layer is 0.2 to 2.0 mm. The back surfacerelease layer (b) of the release liner is structured such that a holdingtime, measured in the following way (i) to (iv), is 2500 minutes orlonger:

(i) a test piece (size: 25 mm in width×100 mm in length), having thesame material as that of the release liner, is provided so as to befixed to a bakelite plate with the back surface release layer (b)oriented upward;

(ii) the pressure-sensitive adhesive tape (size: 25 mm in width×100 mmin length) is provided, and the other surface (2) of thepressure-sensitive adhesive layer is attached to the back surfacerelease layer (b) of the test piece such that a contact area becomes 25mm in width×40 mm in length;

(iii) the pressure-sensitive adhesive tape is pressure-bonded by movinga 5-kg roller one way; and

(iv) a holding time, until the pressure-sensitive adhesive tape dropsoff from the test piece, is measured by applying a load of 1.96 N (0.2kgf) to an end portion of the pressure-sensitive adhesive tape, the endportion not contacting the test piece, in a longitudinal direction ofthe pressure-sensitive adhesive tape and in an environment of an ambienttemperature of 40° C.

According to this aspect, a pressure-sensitive adhesive tape can beachieved, in which oozing of a pressure-sensitive adhesive issuppressed.

Peeling force, occurring when the release liner is peeled from thepressure-sensitive adhesive layer in a 180°-peeling direction, at atensile speed of 300 mm/min, and in an environment of an ambienttemperature of 23° C., may be 1.0 [N/25 mm] or more.

The release liner may include: a base layer containing a polyolefinresin; and a release layer (a) that contains low-density polyethyleneand is provided on at least one side of the base layer so as to contactthe pressure-sensitive adhesive layer.

Alternatively, the release liner may include: a base layer containing apolyolefin resin; a release layer (a) that contains linear low-densitypolyethylene and is provided on one side of the base layer so as tocontact the pressure-sensitive adhesive layer; and aback surface releaselayer (b) that contains linear low-density polyethylene and is providedon the other side of the base layer.

The pressure-sensitive adhesive layer may include: a core layercontaining an acrylic polymer (A), a fine particle (B) and/or a bubble(C); and a surface layer that is provided on one or both sides of thecore layer and contains an acrylic polymer (D) and a (meth)acrylicpolymer (E) having a weight average molecular weight (M_(WE)) of1000≦M_(WE)<30000.

The content of the (meth)acrylic polymer (E) may be 5 to 45 parts bymass, based on 100 parts by mass of the acrylic polymer (D).

Each of the acrylic polymer (A) and the acrylic polymer (D) may containa (meth)acrylic acid alkyl ester as a monomer major component.

Another aspect of the present invention is a tape roll. In the taperoll, the pressure-sensitive adhesive tape is wound into a roll shape.According to this aspect, oozing of the pressure-sensitive adhesive canbe suppressed even in the state of being wound into a roll shape.

According to the present invention, oozing of a pressure-sensitiveadhesive can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a structure of anacrylic pressure-sensitive adhesive tape according to an embodiment;

FIG. 2 is a schematic sectional view illustrating a structure of apressure-sensitive adhesive layer illustrated in FIG. 1;

FIG. 3 is a schematic sectional view illustrating a structure of arelease liner illustrated in FIG. 1;

FIG. 4( a) is a top view of a provided bakelite plate;

FIG. 4( b) is a side view of the bakelite plate illustrated in FIG. 4(a);

FIG. 5( a) is a top view of a state where the release liner is attachedto the bakelite plate by using a double-sided pressure-sensitiveadhesive tape;

FIG. 5( b) is a side view of the state in FIG. 5( a);

FIG. 6( a) is a top view of a state where the acrylic pressure-sensitiveadhesive tape is attached to a second release layer (back surfacerelease layer (b)) of the release liner;

FIG. 6( b) is a side view of the state in FIG. 6( a); and

FIG. 7 is a view illustrating a situation where a test piece issubjected to a creep test.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

Hereinafter, preferred embodiments for carrying out the presentinvention will be described in detail with reference to the accompanyingdrawings and tables.

The shape of a pressure-sensitive adhesive tape according to the presentembodiment is not particularly limited, and it may be a sheet shape inaddition to an elongated one like a tape. Hereinafter, a tape-shapedpressure-sensitive adhesive tape, both the surfaces of which arepressure-sensitive adhesive surfaces, will be described.

FIG. 1 is a schematic sectional view illustrating a structure of anacrylic pressure-sensitive adhesive tape 10 according to an embodiment.The acrylic pressure-sensitive adhesive tape 10 includes: apressure-sensitive adhesive layer 12, both the surfaces of which arepressure-sensitive adhesive surfaces; and a release liner 14 provided onone surface 12 a of the pressure-sensitive adhesive layer.

FIG. 2 is a schematic sectional view illustrating a structure of thepressure-sensitive adhesive layer 12 illustrated in FIG. 1. Thepressure-sensitive adhesive layer 12 includes: a core layer 16; asurface layer 18 a provided on one surface of the core layer 16; and asurface layer 18 b provided on the other surface of the core layer 16.Hereinafter, the surface layers 18 a and 18 b are collectively referredto as a surface layer 18. The core layer 16 has: a pressure-sensitiveadhesive composition 20; a fine particle 22 contained in thepressure-sensitive adhesive composition 20; and a bubble 24 formed inthe pressure-sensitive adhesive composition 20. Alternatively, thepressure-sensitive adhesive composition 20 may contain either the fineparticle 22 or the bubble 24.

FIG. 3 is a schematic sectional view illustrating a structure of therelease liner 14 illustrated in FIG. 1. The release liner 14 includes: abase layer 26; a first release layer (release layer (a)) 28 that isprovided on one side of the base layer 26 and functions as a surfacelayer contacting the one surface 12 a of the pressure-sensitive adhesivelayer 12; and a second release layer (back surface release layer (b)) 30that functions as a surface layer provided on the other side of the baselayer 26.

Hereinafter, the structure of each of the release liner 14 and thepressure-sensitive adhesive layer 12 will be described in detail.

[Release Liner]

The release liner according to the present embodiment has a layeredstructure of at least two layers, one layer of which is a surface layeras a release layer provided on at least one side of the base layer. Therelease layer may be provided directly on the surface of the base layer,or be laminated via another layer such as an adhesive layer.

(Surface Layer)

In the release liner according to the present embodiment, it ispreferable that the first release layer (release layer (a)) 28, which isa surface layer provided on the side contacting the pressure-sensitiveadhesive layer 12, is formed of low-density polyethylene and an olefinelastomer that are major components. The total amount of the low-densitypolyethylene and the olefin elastomer is preferably 60% by mass or more,and more preferably 90% by mass or more, based on the total mass of thesurface layer. By causing the first release layer 28 to have such apolymer structure, peelability can be improved.

The “low-density polyethylene (LDPE)” in the present embodiment refersto the polyethylene whose density (d_(P)) is 900 (kg/m³)≦d_(P)<930(kg/m³) based on JIS K 6922-2. The “low-density polyethylene” in theembodiment includes: so-called “low-density polyethylene” and“ultra-low-density polyethylene” each having long-chain branching, whichcan be obtained by polymerizing an ethylene monomer with a high-pressuremethod; and “linear low-density polyethylene (LLDPE)” (the number ofcarbon atoms in short-chain branching is preferably 1 to 6), which canbe obtained by polymerizing ethylene and a C₃₋₈ α-olefin monomer with alow-pressure method. Among them, the linear low-density polyethylene(LLDPE) is particularly preferred as the low-density polyethylene to beused for the surface layer of the release liner according to the presentembodiment, because physical properties such as peelability can beeasily controlled due to the copolymerization of α-olefin. In theaforementioned LLDPE, 1-hexene and 1-octene are preferred as thecomonomer component to be used along with ethylene.

The olefin elastomer is not particularly limited as far as it isα-olefin or a copolymer containing α-olefin and is a compound exhibitingan elastomeric property; and examples of the olefin elastomer include,for example, an ethylene-α-olefin copolymer, propylene-α-olefincopolymer, ethylene-propylene-diene copolymer, ethylene-vinylacetatecopolymer, polybutene, polyisobutylene, and chlorinated polyethylene,etc.

Among the aforementioned olefin elastomers, an ethylene-α-olefincopolymer elastomer is particularly preferred from the viewpoints ofpeelability and compatibility. In the present embodiment, theethylene-α-olefin copolymer, the density (d) of which is less than 900(kg/m³) based on JIS K 6922-2 (e.g., 860 (kg/m³)⁻d<900 (kg/m³)), shallbe included in the olefin elastomers. The α-olefin component in theethylene-α-olefin copolymer elastomer is not particularly limited, butα-olefins having approximately 3 to 10 carbons, such as propylene andbutene, are preferred, and at least one α-olefin (comonomer), selectedfrom the group consisting of propylene, butene-1,hexene-1,4-methylpentene-1, and the octene-1, can be used.

As the low-density polyethylene and olefin elastomer, commerciallyavailable products can also be used, and examples of the low-densitypolyethylene include, for example, “MORETEC 0628D and 0218CN” (LLDPE)made by Prime Polymer Co., Ltd., and the like. Examples of the olefinelastomer include “TAFMER P” (ethylene-propylene copolymer) made byMitsui Chemicals, Inc., and the like. Among them, “TAFMER P P0180 andP0280” can be preferably used from the viewpoint of a film formingproperty.

The low-density polyethylene and olefin elastomer may be used alone orin combination of two or more thereof, respectively.

In the surface layer of the release liner according to the presentembodiment, the content of the olefin elastomer is preferably 0 to 45parts by mass, more preferably 0 to 40 parts by mass, and still morepreferably 5 to 30 parts by mass, based on 100 parts by mass of thelow-density polyethylene. Peelability is improved by adding the olefinelastomer. On the other hand, if the content is more than 45 parts bymass, the adhesive force with the pressure-sensitive adhesive layerbecomes small, and hence, when the pressure-sensitive adhesive tape iswound into a roll shape, the release liner is likely to slip whenexternal force is applied, the pressure-sensitive adhesive is likely toprotrude, or the surface layer of the release liner is likely to beflexible; thereby processability may be decreased or blocking may becaused.

In addition to the low-density polyethylene and olefin elastomer, thesurface layer of the release liner according to the present embodimentmay contain various additives such as a colorant (pigment, dye), filler,lubricant, anti-aging agent, antioxidant, ultraviolet absorber, flameretardant, and stabilizer, within a range not impairing the advantagesof the present invention.

When the release liner of the present embodiment has a three-layeredstructure in which surface layers are provided on both the surfaces ofthe base layer, the surface layers on both the sides may be formed tocontain polymers or compound compositions different from each other, asfar as the aforementioned issues are satisfied. From the viewpoint ofpreventing curl of the release liner, it is preferable that the surfacelayers on both the sides contain the same polymer as each other, and itis more preferable that they have the same composition as each other.So, it is preferable that the second release layer (back surface releaselayer (b)) 30, provided on the other side of the base layer 26, containslow-density polyethylene, similarly to the first release layer (releaselayer (a)) 28.

(Base Layer)

The base layer 26 of the release liner 14 of the present embodiment isformed by using a polyolefin resin as a major component. The content ofthe polyolefin resin is preferably 50% by mass or more, and morepreferably 80% by mass or more, based on the total mass of the baselayer. Because a polyolefin resin is relatively more flexible than apolyester resin such as polyethylene terephthalate, the followability ofthe release liner to a deformation of an adherend is improved when apolyolefin resin is used in the base layer of the release liner, therebyallowing pop-off or peeling of the release liner, possibly occurringwhen stored or used in a high-temperature environment, to be suppressed.A release liner, in which a polyester resin is used in a base layer,cannot follow a slight deformation of an automobile emblem made of aresin, for example, when stored in the state of being attached to theemblem, or the like, and hence pop-off or peeling of the release linermay be caused, so that productivity may be decreased.

As the aforementioned polyolefin resin, polypropylene (PP) andhigh-density polyethylene (HDPE) are preferred from the viewpoints ofmaintaining the strength of the release liner and improving theprocessability. That is, the base layer of the release liner accordingto the present embodiment contains polypropylene (PP) and/orhigh-density polyethylene (HDPE) preferably in an amount of 50% by massor more, and more preferably in an amount of 80% by mass or more, basedon the total mass of the base layer. Among them, a transparent ortranslucent resin is preferred in an application in which the visibilityfor the facing surface side is required, for example, when beingprocessed, and random polypropylene is more preferred. The “high-densitypolyethylene” in the present embodiment refers to the polyethylene whosedensity is 930 (kg/m³) or more (preferably 942 to 960 (kg/m³)) based onJIS K 6922-2.

As the aforementioned olefin resin, commercially available products canalso be used, and examples of the products include, for example: “NoblenWF836DG3 and FS3611” made by Sumitomo Chemical Co., Ltd., and “NovatecPP EG6D” made by Japan Polypropylene Corporation (above are PP); “HI-ZEX3300F” made by Prime Polymer Co. Ltd., and “Nipolon Hard 4050” made byTOSOH CORPORATION (above are HDPE); and the like.

A colorant, such as a pigment, may be added in the base layer of therelease liner of the present embodiment, from the viewpoint of improvingboth the distinguishability of part numbers, etc., and handling propertyby coloring. As the pigment, publicly-known and commonly-used organicand inorganic pigments can be used depending on the type of desiredcolor. Examples of the pigments include, for example, carbon black, ironoxide, titanium oxide, titan yellow, cobalt blue, cadmium red, azo lakepigments (red, yellow), phthalocyanine pigments, and quinacridonepigments, etc.

An antistatic agent may be added in the base layer of the release linerof the present embodiment, from the viewpoints of improving workabilityand preventing destruction of the release layer. As the antistaticagent, publicly-known and commonly-used a non-ionic antistatic agent,anionic antistatic agent, or cationic antistatic agent can be used.

In addition to the resin components, colorant, and antistatic agent,various additives, such as a filler, lubricant, anti-aging agent,antioxidant, ultraviolet absorber, flame retardant, and stabilizer, maybe blended in the base layer of the release liner of the presentembodiment, within a range not impairing the advantages of the presentinvention.

In the release liner of the present embodiment, the thickness of each ofthe surface layers is 80 μm or less, preferably 30 μm or less, and morepreferably 10 μm or less. When containing an olefin elastomer, thesurface layer of the embodiment becomes flexible. Accordingly, as thethickness of the each surface layer becomes larger, the strength andstiffness of the whole release liner becomes smaller, and there is thetendency that, when being cut, the surface layer stretches and the“cutting quality” is deteriorated. That is, if the thickness thereof ismore than 80 μm, punching processability becomes decreased and aprocessing defect, such as “mustache”, “burr”, or the like, is likely tobe caused. The lower limit of the thickness thereof is not particularlylimited, but when the surface layer is provided by co-extrusion, it ispreferable that the thickness is 5 μm or more, from the viewpoint ofuniform lamination by co-extrusion. When the surface layer is providedby coating, it is preferable that the thickness is approximately 0.1 to5 μm.

In the case of a three-layered structure in which the surface layers areprovided on both the surfaces of the base layer, the ratio between thesurface layers on both the sides (ratio of the thickness of a surfacelayer having a larger thickness to that of a surface layer having asmaller thickness) is preferably 5 or less, and more preferably 3 orless. If the ratio between them is more than 5, curl may be caused inthe release liner.

In the release liner of the present embodiment, the thickness of thebase layer is preferably 30 to 190 μm, and more preferably 50 to 170 μm.The base layer plays the role of providing strength to the releaseliner. If the thickness of the base layer is less than 30 μm, thestrength and stiffness of the release liner become small, and thepunching processability or handling property may be decreased. On theother hand, if the thickness is more than 200 μm, the stiffness becomeslarge and it becomes difficult for the release liner to follow a curvedemblem, etc., and hence pop-off or peeling may be caused.

The thickness (total thickness) of the release liner of the presentembodiment is preferably 50 to 200 μm, and more preferably 100 to 180μm.

The Young's modulus of the release liner of the present embodiment ispreferably 150 to 700 MPa, and more preferably 200 to 500 MPa, from theviewpoint of punching processability.

The release liner of the present embodiment can be manufactured by apublicly-known and commonly-used sheet forming method, such as a meltfilm forming method (T-die method, inflation method), solution filmforming method, or the like. The lamination method of the release linerof the present embodiment is not particularly limited, but apublicly-known and commonly-used method, such as a co-extrusion method,dry lamination method, wet lamination method, or the like, can be used.Among them, a co-extrusion method is preferred from the viewpoint ofproductivity.

The surface layer of the release liner of the present embodiment may besubjected to mat processing. By performing mat processing on the surfaceof the surface layer, the terminal peelability from a pressure-sensitiveadhesive surface and the anti-blocking property can be improved.Examples of the mat processing include, for example: a method ofpolishing the surface of the surface layer with a buff or sandpaper; asandblast treatment in which fine scratches are provided to the surfaceof the surface layer by strongly blowing, against the surface, fineparticles, such as glass beads, carborundum, metal particles, or thelike, along with compressed air; emboss processing by an emboss roll; achemical mat treatment by a chemical; and the like.

In the release liner of the present embodiment, it is preferable thatthe arithmetic mean roughness (Ra) of the surface of the release layer(a), the release layer (a) being provided on one surface (1) of thepressure-sensitive adhesive layer so as to contact the one surface (1),is approximately 0.01 to 5.0 μm, although Ra is also related to thethickness of the later-described pressure-sensitive adhesive layer. Inparticular, when the thickness of the pressure-sensitive adhesive layeris 200 to 2000 μm (0.2 to 2.0 mm), Ra is preferably 0.03 to 2.0 μm, andmore preferably 0.05 to 1.2 μm. If the surface of the release liner istoo coarse, the pressure-sensitive adhesive layer permeates between theconcavities and convexities of the surface of the release liner whilethe pressure-sensitive adhesive layer is contacting the release liner(storage period, etc.), because the pressure-sensitive adhesive layer issoft; and the contact area is increased and the peeling force is changedover time, and hence the stability of the peelability may be decreased.The aforementioned permeation property becomes more remarkable as thethickness of the pressure-sensitive adhesive layer is larger.

In the release liner of the present embodiment, it is preferable thatthe arithmetic mean roughness (Ra) of the surface of the back surfacerelease layer (b) located opposite to the release layer (a) isapproximately 0.03 to 5.0 μm, although Ra is also related to thethickness of the later-described pressure-sensitive adhesive layer. Inparticular, when the thickness of the pressure-sensitive adhesive layeris 200 to 2000 μm (0.2 to 2.0 mm), Ra is preferably 0.05 to 5.0 μm, andmore preferably 0.07 to 2.0 μm. Additionally, it is preferable that thearithmetic mean roughness (Ra) of the surface of the back surfacerelease layer (b) is larger than that of the surface of the releaselayer (a).

If the surface roughness of the surface of the back surface releaselayer (b) is smaller than the aforementioned range, the rewindingproperty may be decreased; on the other hand, if the surface roughnessis larger than the range, the temporal stability of the peeling forcemay be decreased, similarly to the surface roughness on the sidecontacting the pressure-sensitive adhesive layer.

[Pressure-Sensitive Adhesive Layer]

Subsequently, each component of the pressure-sensitive adhesive layer 12will be described in detail. The core layer 16 included in thepressure-sensitive adhesive layer 12 has the pressure-sensitive adhesivecomposition 20 and the fine particle 22, and the bubble 24 is formed inthe core layer 16. Hereinafter, each component of the core layer 16 willbe described in detail.

(Pressure-Sensitive Adhesive Composition)

The acrylic polymer (A) is used as a pressure-sensitive adhesivecomposition that forms the core layer 16. The acrylic polymer (A)contains, as a monomer unit, a (meth)acrylic acid alkyl ester having,for example, a C₁₋₂₀ linear or branched alkyl group in an amount of 50%by mass or more. Alternatively, the acrylic polymer (A) may also have astructure formed only by a (meth)acrylic acid alkyl ester having a C₁₋₂₀alkyl group or by a combination of two or more thereof. The acrylicpolymer (A) can be obtained by subjecting the (meth)acrylic acid alkylester to polymerization (e.g., solution polymerization, emulsionpolymerization, UV polymerization), along with a polymerizationinitiator.

The ratio (R) of the (meth)acrylic acid alkyl ester having a C₁₋₂₀ alkylgroup is approximately 50% by mass≦R≦99.9% by mass, preferablyapproximately 60% by mass≦R≦95% by mass, and more preferablyapproximately 70% by mass≦R≦93% by mass, based on the total mass of themonomer components for preparing the acrylic polymer (A).

Examples of the (meth)acrylic acid alkyl ester having a C₁₋₂₀ alkylgroup include, for example: (meth)acrylic acid C₁₋₂₀ alkyl esters[preferably (meth)acrylic acid C₂₋₁₄ alkyl esters, and more preferably(meth)acrylic acid C₂₋₁₀ alkyl esters], such as (meth)acrylic acidmethyl, (meth)acrylic acid ethyl, (meth)acrylic acid propyl,(meth)acrylic acid isopropyl, (meth)acrylic acid butyl, (meth)acrylicacid isobutyl, (meth)acrylic acid s-butyl, (meth)acrylic acid t-butyl,(meth)acrylic acid pentyl, (meth)acrylic acid isopentyl, (meth)acrylicacid hexyl, (meth)acrylic acid heptyl, (meth)acrylic acid octyl,(meth)acrylic acid 2-ethylhexyl, (2-ethylhexyl(meth)acrylate),(meth)acrylic acid isooctyl, (meth)acrylic acid nonyl, (meth)acrylicacid isononyl, (meth)acrylic acid decyl, (meth)acrylic acid isodecyl,(meth)acrylic acid undecyl, (meth)acrylic acid dodecyl, (meth)acrylicacid tridecyl, (meth)acrylic acid tetradecyl, (meth)acrylic acidpentadecyl, (meth)acrylic acid hexadecyl, (meth)acrylic acid heptadecyl,(meth)acrylic acid octadecyl, (meth)acrylic acid nonadecyl, and(meth)acrylic acid eicosyl, etc. Herein, the (meth)acrylic acid alkylester means an acrylic acid alkyl ester and/or a methacrylic acid alkylester, and all of the “(meth) . . . ” expressions have the same meaning.

Examples of the (meth)acrylic acid esters other than the (meth)acrylicacid alkyl esters include, for example: (meth)acrylic acid esters havingan alicyclic hydrocarbon group, such as cyclopentyl(meth)acrylate,cyclohexyl(meth)acrylate, and isobornyl(meth)acrylate; (meth)acrylicacid esters having an aromatic hydrocarbon group, such asphenyl(meth)acrylate; (meth)acrylic acid esters obtained from terpenecompound derivative alcohols; and the like.

For the purpose of modifying cohesive force, heat resistance, andcross-linking property, etc., the acrylic polymer (A) may contain, ifnecessary, another monomer component (copolymerizable monomer) that iscopolymerizable with the (meth)acrylic acid alkyl ester. Accordingly,the acrylic polymer (A) may contain a copolymerizable monomer along withthe (meth)acrylic acid alkyl ester as a major component. A monomerhaving a polar group can be preferably used as the copolymerizablemonomer.

Specific examples of the copolymerizable monomer include: carboxylgroup-containing monomers, such as acrylate, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid,fumaric acid, crotonic acid, and isocrotonic acid; hydroxylgroup-containing monomers, such as (meth)acrylic acid hydroxyalkylsincluding (meth)acrylic acid hydroxyethyl, (meth)acrylic acidhydroxypropyl, (meth)acrylic acid hydroxybutyl, (meth)acrylic acidhydroxyhexyl, (meth)acrylic acid hydroxyoctyl, (meth)acrylic acidhydroxydecyl, (meth)acrylic acid hydroxy lauryl, and (4-hydroxymethylcyclohexyl)methyl methacrylate; acid anhydride group-containingmonomers, such as maleic acid anhydride and itaconic acid anhydride;sulfonic group-containing monomers, such as styrenesulfonic acid,allylsulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid,(meth)acrylamide propanesulfonic acid, sulfopropyl(meth)acrylate, and(meth)acryloyloxy naphthalenesulfonic acid; phosphate group-containingmonomers, such as 2-hydroxyethyl acryloyl phosphate;(N-substituted)amide monomers, such as (meth)acrylamide,N,N-dialkyl(meth)acrylamides including N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide,N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, andN,N-di(t-butyl)(meth)acrylamide, etc., N-ethyl(meth)acrylamide,N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide,N-n-butyl(meth)acrylamide, N-methylol(meth)acrylamide,N-ethylol(meth)acrylamide, N-methylol propane(meth)acrylamide,N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide,N-butoxymethyl(meth)acrylamide, and N-acryloyl morpholine; succinimidemonomers, such as N-(meth)acryloyloxy methylene succinimide,N-(meth)acryloyl-6-oxy hexamethylene succinimide, andN-(meth)acryloyl-8-oxy hexamethylene succinimide; maleimide monomers,such as N-cyclohexyl maleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenyl maleimide; itaconimide monomers, such asN-methylitaconimide, N-ethylitaconimide, N-butylitaconimide,N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide,and N-laurylitaconimide; nitrogen-containing heterocyclic monomers, suchas N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine,N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine,N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole,N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine,N-(meth)acryloyl pyrrolidine, N-vinyl morpholine, N-vinyl-2-piperidone,N-vinyl-3-morpholinone, N-vinyl-2-caprolactam,N-vinyl-1,3-oxazine-2-one, N-vinyl-3,5-morpholinedione,N-vinyl pyrazole,N-vinyl isoxazole, N-vinyl thiazole, N-vinyl isothiazole, and N-vinylpyridazine; N-vinyl carboxylic acid amides; lactam monomers, such asN-vinyl caprolactam; cyanoacrylate monomers, such as acrylonitrile andmethacrylonitrile; (meth)acrylic acid aminoalkyl monomers, such as(meth)acrylic acid aminoethyl, (meth)acrylic acidN,N-dimethylaminoethyl, (meth)acrylic acid N,N-dimethylaminoethyl, and(meth)acrylic acid t-butylaminoethyl; (meth)acrylic acid alkoxy alkylmonomers, such as (meth)acrylic acid methoxyethyl and (meth)acrylic acidethoxyethyl; styrene monomers, such as styrene and α-methylstyrene;epoxy group-containing acrylic monomers, such as (meth)acrylic acidglycidyl; glycol acrylic ester monomers, such as (meth)acrylic acidpolyethylene glycol, (meth)acrylic acid polypropylene glycol,(meth)acrylic acid methoxy ethylene glycol, and (meth)acrylic acidmethoxy polypropylene glycol; acrylic acid ester monomers having aheterocycle, halogen atom, silicon atom, or the like, such as(meth)acrylic acid tetrahydrofurfuryl, fluorine atom-containing(meth)acrylate, and silicone(meth)acrylate; olefin monomers, such asisoprene, butadiene, and isobutylene; vinyl ether monomers, such asmethyl vinyl ether and ethyl vinyl ether; vinyl esters, such as vinylacetate and vinyl propionate; aromatic vinyl compounds, such as vinyltoluene and styrene; olefins or dienes, such as ethylene, butadiene,isoprene, and isobutylene; vinyl ethers, such as vinyl alkyl ether;vinyl chloride; sulfonic acid group-containing monomers, such as vinylsulfonate sodium; imide group-containing monomers, such as cyclohexylmaleimide and isopropyl maleimide; isocyanate group-containing monomers,such as 2-isocyanate ethyl(meth)acrylate; amide group-containing vinylmonomers, such as N-acryloyl morpholine; and the like. Thesecopolymerizable monomer can be used alone or in combination of two ormore thereof.

The use amount of the copolymerizable monomer is not particularlylimited, but the copolymerizable monomer can be contained in an amountusually within a range of approximately 0.1 to approximately 40% bymass, preferably within a range of approximately 0.5 to approximately30% by mass, and more preferably within a range of approximateky 1 toapproximately 20% by mass, based on the total mass of the monomercomponents for preparing the acrylic polymer (A).

By containing approximately 0.1% by mass or more of the copolymerizablemonomer, a decrease in the cohesive force of the acrrylicpressure-sensitive adhesive that forms the core layer 20 can beprevented, and high shear force can be obtained. Further, by containingthe copolymerizable monomer in an amount of approximately 40% by mass orless, the cohesive force of the acrylic pressure-sensitive adhesive thatforms the core layer 20 can be prevented from becoming too large, andthe tackiness at normal temperature (25° C.) can be improved.

A polyfunctional monomer may be contained, if necessary, in the acrylicpolymer (A) in order to adjust the cohesive force of an acrylicpressure-sensitive adhesive tape.

Examples of the polyfunctional monomer include, for example,(poly)ethylene glycol di(meth)acrylate, (poly)propylene glycoldi(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, tetramethylol methane tri(meth)acrylate,allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxyacrylate, polyester acrylate, urethane acrylate, butyl di(meth)acrylate,and hexyl di(meth)acrylate, etc. Among them, trimethylolpropanetri(meth)acrylate, hexanediol di(meth)acrylate, and dipentaerythritolhexa(meth)acrylate can be preferably used. The polyfunctional(meth)acrylate can be used alone or in combination of two or morethereof.

The use amount of the polyfunctional monomer is changed depending on themolecular weight or the number of functional groups thereof, but thepolyfunctional monomer is added in an amount within a range ofapproximately 0.01 to approximately 3.0% by mass, preferably within arange of approximately 0.02 to approximately 2.0% by mass, and morepreferably within a range of approximately 0.03 to approximately 1.0% bymass, based on the total mass of the monomer components for preparingthe (meth)acrylic polymer (A).

If the use amount of the polyfunctional monomer is more thanapproximately 3.0% by mass based on the total mass of the monomercomponents for preparing the acrylic polymer (A), for example, thecohesive force of the acrylic pressure-sensitive adhesive that forms thecore layer 16 becomes too large, and hence the adhesive force may bedecreased. On the other hand, if the use amount is less thanapproximately 0.01% by mass, for example, the cohesive force of theacrylic pressure-sensitive adhesive that forms the core layer 20 may bedecreased.

(Polymerization Initiator)

In preparing the acrylic polymer (A), the acrylic polymer (A) can beeasily formed by a curing reaction using heat or ultraviolet rays withthe use of a polymerization initiator, such as a thermal polymerizationinitiator, photo-polymerization initiator (photo-initiator), or thelike. In particular, a photo-polymerization initiator can be preferablyused in terms of the advantage that a polymerization time can beshortened. The polymerization initiators can be used alone or incombination of two or more thereof.

Examples of the thermal polymerization initiator include, for example:azo polymerization initiators [e.g., 2,2′-azobisisobutyronitrile,2,2′-azobis-2-methylbutyronitrile, 2,2′-azobis(2-methylpropionicacid)dimethyl, 4,4′-azobis-4-cyanovalerianic acid, azobisisovaleronitrile, 2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis[2-(5-methyl-2-imidazoline-2-yl) propane]dihydrochloride,2,2′-azobis(2-methylpropionamidine)disulfate, and2,2′-azobis(N,N′-dimethyleneisobutylamidine)dihydrochloride, etc.];peroxide polymerization initiators (e.g., dibenzoyl peroxide, t-butylpermaleate, and lauroyl peroxide, etc.); redox polymerizationinitiators; and the like.

The use amount of the thermal polymerization initiator is notparticularly limited, but only has to be within a conventional range inwhich it can be used as a thermal polymerization initiator.

The photo-polymerization initiator is not particularly limited, but, forexample, a benzoin ether photo-polymerization initiator, acetophenonephoto-polymerization initiator, α-ketol photo-polymerization initiator,aromatic sulfonyl chloride photo-polymerization initiator, photoactiveoxime photo-polymerization initiator, benzoin photo-polymerizationinitiator, benzyl photo-polymerization initiator, benzophenonephoto-polymerization initiator, ketal photo-polymerization initiator,thioxanthone photo-polymerization initiator, acylphosphine oxidephoto-polymerization initiator, or the like, can be used.

Specific examples of the benzoin ether photo-polymerization initiatorinclude, for example, benzoin methyl ether, benzoin ethyl ether, benzoinpropyl ether, benzoin isopropyl ether, benzoin isobutyl ether,2,2-dimethoxy-1,2-diphenylethane-1-one [product name: IRGACURE 651 madeby Ciba Specialty Chemicals Corp.], and anisole methyl ether, etc.Specific examples of the acetophenone photo-polymerization initiatorinclude, for example, 1-hydroxycyclohexyl-phenyl-ketone [product name:IRGACURE 184 made by Ciba Specialty Chemicals Corp.], 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one[product name: IRGACURE 2959 made by Ciba Specialty Chemicals Corp.],2-hydroxy-2-methyl-1-phenyl-propane-1-one [product name: DAROCUR 1173made by Ciba Specialty Chemicals Corp.], and methoxy acetophenone, etc.Specific examples of α-ketol photo-polymerization initiator include, forexample, 2-methyl-2-hydroxy propiophenone and1-[4-(2-hydroxyethyl)-phenyl]-2-hydroxy-2-methylpropane-1-one, etc.Specific examples of the aromatic sulfonyl chloride photo-polymerizationinitiator include, for example, 2-naphthalene sulfonyl chloride, etc.Specific examples of the photoactive oxime photo-polymerizationinitiator include, for example,1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime, etc.

Specific examples of the benzoin photo-polymerization initiator include,for example, benzoin, etc. Specific examples of the benzylphoto-polymerization initiator include, for example, benzyl, etc.Specific examples of the benzophenone photo-polymerization initiatorsinclude, for example, benzophenone, benzoylbenzoic acid,3,3′-dimethyl-4-methoxybenzophenone, polyvinyl benzophenone, andα-hydroxy cyclohexyl phenyl ketone, etc. Specific examples of the ketalphoto-polymerization initiator include, for example, benzyl dimethylketal, etc. Specific examples of the thioxanthone photo-polymerizationinitiato include, for example, thioxanthone, 2-chlorothioxanthone,2-methyl thioxanthone, 2,4-dimethyl thioxanthone, isopropylthioxanthone, 2,4-dichloro thioxanthone, 2,4-diethyl thioxanthone,isopropyl thioxanthone, 2,4-diisopropyl thioxanthone, and dodecylthioxanthone, etc.

Examples of the acylphosphine photo-polymerization initiator include,for example, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide,bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl)phosphine oxide,bis(2,6-dimethoxybenzoyl)-n-butyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-(2-methylpropane-1-yl)phosphine oxide,bis(2,6-dimethoxybenzoyl)-(1-methylpropane-1-yl)phosphine oxide,bis(2,6-dimethoxybenzoyl)-t-butylphosphine oxide,bis(2,6-dimethoxybenzoyl)cyclohexylphosphine oxide,bis(2,6-dimethoxybenzoyl)octylphosphine oxide,bis(2-methoxybenzoyl)(2-methylpropane-1-yl)phosphine oxide,bis(2-methoxybenzoyl)(1-methylpropane-1-yl)phosphine oxide,bis(2,6-diethoxybenzoyl)(2-methylpropane-1-yl)phosphine oxide,bis(2,6-diethoxybenzoyl)(1-methylpropane-1-yl)phosphine oxide,bis(2,6-dibutoxybenzoyl)(2-methylpropane-1-yl)phosphine oxide,bis(2,4-dimethoxybenzoyl)(2-methypropane-1-yl)phosphine oxide,bis(2,4,6-trimethylbenzoyl)(2,4-dipentoxyphenyl)phosphine oxide,bis(2,6-dimethoxybenzoyl)benzyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylpropyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylethyl phosphine oxide,bis(2,6-dimethoxybenzoyl)benzyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylpropyl phosphine oxide,bis(2,6-dimethoxybenzoyl)-2-phenylethyl phosphine oxide,2,6-dimethoxybenzoyl benzylbutylphosphine oxide, 2,6-dimethoxybenzoylbenzyloctylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,5-diisopropylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2-methylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-4-methylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,5-diethylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,3,5,6-tetramethylphenylphosphin e oxide,bis(2,4,6-trimethyl benzoyl)-2,4-di-n-butoxy phenylphosphine oxide,2,4,6-trimethylbenzoyl diphenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,bis(2,4,6-trimethylbenzoyl)isobutylphosphine oxide,2,6-dimethoxybenzoyl-2,4,6-trimethylbenzoyl-n-butylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-2,4-dibutoxyphenylphosphine oxide,1,10-bis[bis(2,4,6-trimethylbenzoyl)phosphine oxide]decane, andtri(2-methylbenzoyl)phosphine oxide, etc.

The use amount of the photo-polymerization initiator is not particularlylimited, but the photo-polymerization initiator is combined, forexample, in an amount within a range of approximately 0.01 toapproximately 5 parts by mass, and preferably within a range ofapproximately 0.05 to approximately 3 parts by mass, based on 100 partsby mass of the monomer components for preparing the acrylic polymer (A).

If the use amount of the photo-polymerization initiator is less than0.01 parts by mass, a polymerization reaction may become insufficient.On the other hand, if the use amount of the photo-polymerizationinitiator is more than 5 parts by mass, an ultraviolet ray does notreach the inside of the pressure-sensitive adhesive layer because thephoto-polymerization initiator absorbs an ultraviolet ray; and hence therate of polymerization is decreased or the molecular weight of theproduced polymer becomes small. Accordingly, the cohesive force of theproduced pressure-sensitive adhesive layer becomes small, and part ofthe pressure-sensitive adhesive layer remains on a film when thepressure-sensitive adhesive layer is peeled from the film, so that thefilm may not be reused. The photo-polymerization initiators may be usedalone or in combination of two or more thereof.

Besides the aforementioned polyfunctional monomers, a cross-linkingagent can also be used in order to adjust the cohesive force.Commonly-used cross-linking agents can be used as the cross-linkingagent. Examples of the cross-linking agent include, for example: anepoxy cross-linking agent, isocyanate cross-linking agent, siliconecross-linking agent, oxazoline cross-linking agent, aziridinecross-linking agent, silane cross-linking gent, alkyl-etherifiedmelamine cross-linking agent, and metal chelate cross-linking agent,etc. In particular, an isocyanate cross-linking agent and an epoxycross-linking agent can be preferably used.

Specific examples of the isocyanate cross-linking agent include tolylenediisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,xylylene diisocyanate, hydrogenated xylylene diisocyanate,diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate,tetramethyl xylylene diisocyanate, naphthalene diisocyanate,triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, andthese adducts with polyols, such as trimethylolpropane. Alternatively, acompound containing, within a molecule thereof, at least one or moreisocyanate groups and at least one or more unsaturated bonds,specifically, 2-isocyanate ethyl(meth)acrylate, or the like, can be usedas the isocyanate cross-linking agent. Among them, the use of thecompound containing, within a molecule thereof, at least one or moreisocyanate groups and at least one or more unsaturated bonds as theisocyanate cross-linking agent is preferable from the viewpoint offurther exhibiting the advantages of the present invention.

Examples of the epoxy cross-linking agent include: bisphenol A,epichlorohydrin type epoxy resin, ethyleneglycidylether, polyethyleneglycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidylether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidylether, diglycidyl aniline, diamine glycidyl amine,N,N,N′,N′-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N′-diamineglycidyl aminomethyl)cyclohexane, etc.

In the present embodiment, the acrylic polymer (A) can also be preparedas a partial polymer (acrylic polymer syrup) that can be obtained byradiating ultraviolet (UV) rays onto a mixture in which theaforementioned monomer components and the polymerization initiator havebeen combined, so that the monomer components are partially polymerized.The weight average molecular weight (Mw) of the acrylic polymer (A) is,for example, within a range of 30000 to 5000000.

(Fine Particle)

In the present embodiment, fine particles (B) can be added to theacrylic polymer (A) that forms the core layer. The fine particle (B) hasoperational effects of improving the shear adhesive force andprocessability of the acrylic pressure-sensitive adhesive tape or sheetmade of the acrylic pressure-sensitive adhesive.

Examples of the fine particle (B) include: metallic particles made ofcopper, nickel, aluminum, chromium, iron, and stainless steel, etc., andmetal oxide particles made of them; carbide particles made of siliconcarbide, boron carbide, and carbon nitride, etc.; nitride particles madeof aluminum nitride, silicon nitride, and boron nitride, etc.; glassparticles; ceramic particles represented by oxides, such as alumina andzirconium, etc.; inorganic fine particles made of calcium carbide,aluminum hydroxide, glass, and silica, etc.; natural material particles,such as volcanic Shirasu and sand, etc.; polymer particles made ofpolystyrene, polymethyl methacrylate, phenol resin, benzoguanamineresin, urea resin, silicone resin, nylon, polyester, polyurethane,polyethylene, polypropylene, polyamide, and polyimide, etc.; organichollow bodies made of vinylidene chloride, and acrylic, etc.; organicspheres, such as nylon bead, acrylic bead, and silicone bead; and thelike.

Hollow fine particles can be preferably used as the fine particle (B).Among the hollow fine particles, a hollow inorganic fine particle can bepreferably used from the viewpoints of an efficiency of thepolymerization using an ultraviolet reaction and weight. Examples of thehollow inorganic fine particle include: glass balloons, such as a hollowglass balloon (also referred to as a hollow glass microsphere); hollowballoons made of metallic compounds, such as a hollow aluminum balloon;hollow balloons made of porcelain, such as a hollow ceramic balloon; andthe like. High-temperature adhesive force can be improved by using theaforementioned hollow glass balloons, without impairing otherproperties, such as shear force and holding force.

Examples of the hollow glass balloon (hollow glass microsphere) include,for example, the products: with the name of “Glass Microballoon” (madeby FUJI SILYSIA CHEMICAL, Ltd.); with the names of “CEL-STAR Z-20”,“CEL-STAR Z-27”, “CEL-STAR CZ-31T”, “CEL-STAR Z-36”, “CEL-STAR Z-39”,“CEL-STAR T-36”, and “CEL-STAR PZ-6000” (all of which are made by TokaiKogyo Co., Ltd.); with the name of “SILUX FINE BALLOON” (made byFINE-BALLOON Ltd.); and the like.

The size (average particle size) of the fine particle (B) is notparticularly limited, but can be selected from a range of, for example,1 to 500 μm, preferably from a range of 5 to 200 μm, and more preferablyfrom a range of 10 to 150 μm.

The specific gravity of the fine particle (B) is not particularlylimited, but can be selected from a range of, for example, 0.1 to 1.8g/cm³, preferably from a range of 0.2 to 1.5 g/cm³, and more preferablyfrom a range of 0.2 to 0.5 g/cm³.

If the specific gravity of the fine particle (B) is smaller than 0.1g/cm³, floating of the fine particles (B) becomes large when the fineparticles are combined into the acrylic pressure-sensitive adhesive andthey are mixed, and hence it may be difficult to uniformly scatter thefine particles. Additionally, because the strength of the glass becomeslow, it will easily crack. Conversely, if the specific gravity thereofis larger than 1.8 g/cm³, the transmission rate of an ultraviolet ray isdecreased, and hence there is the fear that the efficiency of theultraviolet reaction may be decreased. Additionally, the acrylicpressure-sensitive adhesive becomes heavy and workability isdeteriorated.

The use amount of the fine particles (B) is not particularly limited,but if it is, for example, less than 10% by volume, based on the wholevolume of the core layer, the effects of adding the fine particlesbecome low; on the other hand, if it is more than 50% by volume, theadhesive force is decreased.

(Bubble)

In the present embodiment, the bubbles (C) can be added to the acrylicpolymer (A) that forms the core layer. By containing the bubbles (C) inthe core layer, the acrylic pressure-sensitive adhesive (acrylicpressure-sensitive adhesive tape) can exhibit good adhesiveness to acurved surface and concave-convex surface, and also exhibit goodresistance to resilience.

It is desirable that the bubbles (C) contained in the core layer arebasically closed-cell type bubbles, but closed-cell type bubbles andinterconnected-cell type bubbles may coexist.

Although the bubble (C) usually has a spherical shape (in particular, atrue spherical shape), the shape does not necessarily have to be a truespherical shape, and there may be concavities and convexities on thesurface of a spherical shape. The average bubble size (diameter) of thebubble (C) is not particularly limited, but can be selected, forexample, from a range of 1 to 1000 μm, preferably from a range of 10 to500 μm, and more preferably from a range of 30 to 300

A gas component contained in the bubble (C) (gas component that formsthe bubble (C); hereinafter, sometimes referred to as bubble-forminggas) is not particularly limited, but various gas components, such asinactive gases including nitrogen, carbon dioxide, and argon, and air,can be used. When a polymerization reaction is performed in a statewhere a bubble-forming gas is contained, it is important that the gasthat forms the bubble does not hamper the reaction. Nitrogen can bepreferably used as the bubble-forming gas in terms of not hampering thepolymerization reaction and cost.

The amount of the bubbles (C) contained in the core layer is notparticularly limited, but can be appropriately selected in accordancewith the application and use of the tape, etc. The amount thereof is,for example, 5 to 50% by volume, and preferably 8 to 40% by volume,based on the whole volume of the core layer containing the bubbles. Ifthe mixing amount of the bubbles is less than 5% by volume, the effectsof mixing the bubbles cannot be obtained. Conversely, if the mixingamount is more than 50% by volume, the bubbles each penetrating the corelayer are present, and hence the adhesive performance or the appearanceis decreased.

In the core layer containing the bubbles (C), the form in which thebubble is formed is not particularly limited. As the core layercontaining the bubbles, a core layer in which bubbles are formed can beformed, for example: (1) by using a core layer in which a gas componentthat forms the bubble (bubble-forming gas) is mixed beforehand; or (2)by mixing a foaming agent in the core layer. In the case of theaforementioned method of (2) where a core layer in which bubbles areformed is formed by using a core layer containing a foaming agent, thefoaming agent is not particularly limited, but for example, can beappropriately selected from publicly-known foaming agents. As thefoaming agent, for example, a heat-expandable microsphere, etc., can beused.

(Other Components)

Other than the aforementioned components, a thickener, thixotropicagent, and filler, etc., may be added to the core layer, if necessary.Examples of the thickener include acrylic rubber, epichlorohydrinrubber, and butyl rubber, etc. Examples of the thixotropic agent includecolloid silica and polyvinylpyrrolidone, etc. Examples of the fillerinclude calcium carbonate, titanium oxide, and clay, etc. Other thanthese, a plasticizer, anti-aging agent, and antioxidant, etc., may beappropriately added thereto. Additives to be added should not be limitedthereto.

(Surface Layer)

The components of the surface layer 18 include: as a pressure-sensitiveadhesive composition, an acrylic polymer (D); and as a tackifying resin,a (meth)acrylic polymer (E) having a weight average molecular weight(M_(WE)) of 1000≦M_(WE)<30000. The acrylic polymer (D) to be used in thesurface layer 18 can be selected from the compounds (various monomercomponents) exemplifying the acrylic polymer (A) in the core layer 16.The acrylic polymer (D) to be used in the surface layer 18 may or maynot have the same components and composition ratios as those of theacrylic polymer (A) in the core layer 16. The acrylic polymer (D) can beprepared by using the same polymerization initiator and polymerizationmethod as those of the acrylic polymer (A) that forms the core layer.Hereinafter, the (meth)acrylic polymer (E) will be described in detail.

[(Meth)Acrylic Polymer (E)]

The (meth)acrylic polymer (E) is a polymer having a weight averagemolecular weight smaller than that of the acrylic polymer (D), andfunctions as a tackifying resin and has the advantage that inhibition ofpolymerization is hardly caused when UV polymerization is performed. Byblending the (meth)acrylic polymer (E) in the pressure-sensitiveadhesive composition that forms the surface layer, the adhesiveness ofthe acrylic pressure-sensitive adhesive tape to an adherend having lowpolarity, which is made of polyethylene, polypropylene, or the like, canbe remarkably improved. For example, the (meth)acrylic polymer (E)contains, as a monomer unit, a (meth)acrylic acid ester.

Examples of such a (meth)acrylic acid ester include: (meth)acrylic acidalkyl esters, such as (meth)acrylic acid methyl, (meth)acrylic acidethyl, (meth)acrylic acid propyl, (meth)acrylic acid isopropyl,(meth)acrylic acid butyl, (meth)acrylic acid isobutyl, (meth)acrylicacid s-butyl, (meth)acrylic acid t-butyl, (meth)acrylic acid pentyl,(meth)acrylic acid isopentyl, (meth)acrylic acid hexyl, (meth)acrylicacid-2-ethylhexyl, (meth)acrylic acid heptyl, (meth)acrylic acid octyl,(meth)acrylic acid isooctyl, (meth)acrylic acid nonyl, (meth)acrylicacid isononyl, (meth)acrylic acid decyl, (meth)acrylic acid isodecyl,(meth)acrylic acid undecyl, and (meth)acrylic acid dodecyl; esters of(meth)acrylic acids with alicyclic alcohols, such as (meth)acrylic acidcyclohexyl and (meth)acrylic acid isobornyl; (meth)acrylic acid arylesters, such as (meth)acrylic acid phenyl and (meth)acrylic acid benzyl;(meth)acrylic acid esters obtained from terpene compound derivativealcohols; and the like. These (meth)acrylic acid esters can be usedalone or in combination.

Alternatively, the (meth)acrylic polymer (E) can also be obtained bycopolymerizing another monomer component (copolymerizable monomer) thatis copolymerizable with the (meth)acrylic acid ester, in addition to the(meth)acrylic acid ester component unit.

Examples of the another monomer that is copolymerizable with the(meth)acrylic acid ester include: (meth)acrylic acid alkoxy alkylmonomers, such as (meth)acrylic acid methoxyethyl, (meth)acrylic acidethoxyethyl, (meth)acrylic acid propoxyethyl, (meth)acrylic acidbutoxyethyl, and (meth)acrylic acid ethoxypropyl; salts, such as(meth)acrylic acid alkali metal salt; di(meth)acrylic acid estermonomers of (poly)alkylene glycols, such as di(meth)acrylic acid esterof ethylene glycol, di(meth)acrylic acid ester of diethylene glycol,di(meth)acrylic acid ester of triethylene glycol, di(meth)acrylic acidester of polyethylene glycol, di(meth)acrylic acid ester of propyleneglycol, di(meth)acrylic acid ester of dipropylene glycol, anddi(meth)acrylic acid ester of tripropylene glycol; poly(meth)acrylicacid ester monomers, such as trimethylolpropane tri(meth)acrylic acidester; vinyl esters, such as vinyl acetate and vinyl propionate;halogenated vinyl compounds, such as vinylidene chloride and(meth)acrylic acid-2-chloroethyl; oxazoline group-containingpolymerizable compounds, such as 2-vinyl-2-oxazoline,2-vinyl-5-methyl-2-oxazoline, and 2-isopropenyl-2-oxazoline; aziridinegroup-containing polymerizable compounds, such as(meth)acryloylaziridine and (meth)acrylic acid-2-aziridinylethyl; epoxygroup-containing vinyl monomers, such as allyl glycidyl ether,(meth)acrylic acid glycidyl ether, and (meth)acrylic acid-2-ethylglycidyl ether; hydroxyl group-containing vinyl monomers, such as(meth)acrylic acid-2-hydroxyethyl, (meth)acrylic acid-2-hydroxypropyl,monoesters of (meth)acrylic acids with polypropylene glycol orpolyethylene glycol, and adducts of lactones with (meth)acrylicacid-2-hydroxyethyl; fluorine-containing vinyl monomers, such asfluorine-substituted (meth)acrylic acid alkyl ester; acid anhydridegroup-containing monomers, such as maleic acid anhydride and itaconicacid anhydride; aromatic vinyl compound monomers, such as styrene,α-methylstyrene, and vinyl toluene; reactive halogen-containing vinylmonomers, such as 2-chloroethyl vinyl ether and monochloro vinylacetate; amide group-containing vinyl monomers, such as(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N-methylol(meth)acrylamide, N-ethylol(meth)acrylamide,N-methylolpropane(meth)acrylamide, N-methoxyethyl(meth)acrylamide,N-butoxymethyl(meth)acrylamide, and N-acryloyl morpholine; succinimidemonomers, such as N-(meth)acryloyloxy methylene succinimide,N-(meth)acryloyl-6-oxy hexamethylene succinimide, andN-(meth)acryloyl-8-oxy hexamethylene succinimide; maleimide monomers,such as N-cyclohexyl maleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenyl maleimide; itaconimide monomers, such asN-methylitaconimide, N-ethylitaconimide, N-butylitaconimide,N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide,and N-laurylitaconimide; nitrogen-containing heterocyclic monomers, suchas N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine,N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine,N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole,N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine,N-(meth)acryloylpyrrolidine, N-vinyl morpholine, N-vinyl pyrazole,N-vinyl isoxazole, N-vinyl thiazole, N-vinyl isothiazole, and N-vinylpyridazine; N-vinyl carboxylic acid amides; lactam monomers, such asN-vinyl caprolactam; cyanoacrylate monomers, such as(meth)acrylonitrile; (meth)acrylic acid aminoalkyl monomers, such as(meth)acrylic acid aminoethyl, (meth)acrylic acidN,N-dimethylaminoethyl, (meth)acrylic acid N,N-dimethylaminoethyl, and(meth)acrylic acid t-butylaminoethyl; imide group-containing monomers,such as cyclohexyl maleimide and isopropyl maleimide; isocyanategroup-containing monomers, such as 2-isocyanate ethyl(meth)acrylate;organic silicon-containing vinyl monomers, such asvinyltrimethoxysilane, γ-methacryloxpropyl trimethoxy silane,allyltrimethoxysilane, trimethoxysilylpropylallylamine, and 2-methoxyethoxy trimethoxy silane; hydroxyl group-containing monomers, such as(meth)acrylic acid hydroxyalkyls including (meth)acrylic acidhydroxyethyl, (meth)acrylic acid hydroxypropyl, (meth)acrylic acidhydroxybutyl, (meth)acrylic acid hydroxyhexyl, (meth)acrylic acidhydroxyoctyl, (meth)acrylic acid hydroxydecyl, (meth)acrylic acidhydroxy lauryl, and (4-hydroxymethyl cyclohexyl)methyl methacrylate;acrylic acid ester monomers having a heterocycle, halogen atom, siliconatom, or the like, such as (meth)acrylic acid tetrahydrofurfuryl,fluorine atom-containing (meth)acrylate, and silicone(meth)acrylate;olefin monomers, such as isoprene, butadiene, and isobutylene; vinylether monomers, such as methyl vinyl ether and ethyl vinyl ether;olefins or dienes, such as ethylene, butadiene, isoprene, andisobutylene; vinyl ethers, such as vinyl alkyl ether; vinyl chloride;and others, such as macromonomers having a radically polymerizable vinylgroup at the monomer end to which a vinyl group has been polymerized;and the like. These monomers can be copolymerized, alone or incombination thereof, with the (meth)acrylic acid esters.

In the acrylic pressure-sensitive adhesive composition of the presentembodiment, examples of the (meth)acrylic polymer (E) include, forexample: a copolymer of cyclohexyl methacrylate (CHMA) and isobutylmethacrylate (IBMA), that of cyclohexylmethacrylate (CHMA) and isobornylmethacrylate (IBXMA), that of cyclohexyl methacrylate (CHMA) andacryloyl morpholine (ACMO), that of cyclohexyl methacrylate (CHMA) anddiethylacrylamide (DEAA), that of dicyclopentanyl methacrylate (DCPMA)and isobornyl methacrylate (IBXMA), homopolymer of dicyclopentanylmethacrylate (DCPMA), that of cyclohexyl methacrylate (CHMA), that ofisobornylmethacrylate (IBXMA), that of isobornyl acrylate (IBXA), thatof dicyclopentanyl acrylate (DCPA), that of 1-adamantyl methacrylate(ADMA), and that of 1-adamantyl acrylate (ADA), etc.

It is preferable that the (meth)acrylic polymer (E) contains, as amonomer unit, an acrylic monomer having a relatively bulky structure,represented by: (meth)acrylate whose alkyl group has a branchedstructure, such as t-butyl(meth)acrylate; ester of (meth)acrylic acidwith alicyclic alcohol, such as cyclohexyl(meth)acrylate and(meth)acrylic acid isobornyl; and (meth)acrylate having a cyclicstructure, such as (meth)acrylic acid aryl ester including (meth)acrylicacid phenyl and (meth)acrylic acid benzyl. By making the (meth)acrylicpolymer (E) have such a bulky structure, the adhesiveness of the acrylicpressure-sensitive adhesive tape can be further improved. A monomerhaving a cyclic structure has a large effect in terms of bulkiness, anda monomer containing multiple rings further has a larger effect. Inaddition, when UV polymerization is adopted in synthesizing the(meth)acrylic polymer (E) or in producing the pressure-sensitiveadhesive composition, it is preferable to use a monomer having asaturated bond, in terms that inhibition of polymerization is hardlycaused. In that case, (meth)acrylate whose alkyl group has a branchedstructure, or an ester thereof with an alicyclic alcohol can bepreferably used as a monomer that forms the (meth)acrylic polymer (E).

The (meth)acrylic polymer (E) may further contain, as a monomer unit, a(meth)acrylic monomer having, for example, an alicyclic structure ofthree or more rings. By making the (meth)acrylic polymer (E) have such abulky structure as the alicyclic structure of three or more rings, theadhesiveness of the acrylic pressure-sensitive adhesive tape can befurther improved. In particular, the adhesiveness to an adherend havinglow polarity made of polyethylene, polypropylene, or the like, can beimproved more remarkably. The (meth)acrylic polymer (E) may be ahomopolymer of the (meth)acrylic monomer having an alicyclic structureof three or more rings, or may be a copolymer between the (meth)acrylicmonomer having an alicyclic structure of three or more rings and the(meth)acrylic acid ester monomer or copolymerizable monomer.

The (meth)acrylic monomer is a (meth)acrylic acid ester represented by,for example, the following general formula (1):

CH₂═C(R⁴)COOR⁵  (1)

[wherein, R⁴ represents a hydrogen atom or a methyl group and R⁵ analicyclic hydrocarbon group having an alicyclic structure of three ormore rings.]

It is preferable that the alicyclic hydrocarbon group has athree-dimensional structure, such as a bridged ring structure. By makingthe (meth)acrylic polymer (E) have an alicyclic structure of three ormore rings that has a bridged ring structure, as stated above, theadhesiveness of the acrylic pressure-sensitive adhesive tape can befurther improved. In particular, the adhesiveness to an adherend havinglow polarity made of polyethylene, polypropylene, or the like, can beimproved more remarkably. Further, resistance to resilience and aholding property can be both satisfied. That is, by making the(meth)acrylic polymer (E) have an alicyclic structure of three or morerings that has a bridged ring structure, an acrylic pressure-sensitiveadhesive tape can be obtained, in which pressure-sensitive adhesiveforce, resistance to resilience, and a holding property are combined ata high level. Examples of the alicyclic hydrocarbon group having abridged ring structure include, for example: a dicyclopentanyl grouprepresented by the following formula (2a); a dicyclopentenyl grouprepresented by the following formula (2b); an adamantyl grouprepresented by the following formula (2c); a tricyclopentanyl grouprepresented by the following formula (2d); and a tricyclopentenyl grouprepresented by the following formula (2e), etc. When UV polymerizationis adopted in synthesizing the (meth)acrylic polymer (E) or in producingthe pressure-sensitive adhesive composition, a (meth)acrylic monomerhaving a saturated structure, such as the dicyclopentanyl grouprepresented by the following formula (2a), the adamantyl grouprepresented by the following formula (2c), the tricyclopentanyl grouprepresented by the following formula (2d), or the like, of the(meth)acrylic monomers having an alicyclic structure of three or morerings that has a bridged ring structure, can be particularly andpreferably used as a monomer for forming the (meth)acrylic polymer (B),from the viewpoint of hardly causing inhibition of polymerization.

Examples of such a (meth)acrylic monomer having an alicyclic structureof three or more rings that has a bridged ring structure include(meth)acrylic acid esters, such as dicyclopentanyl methacrylate,dicyclopentanyl acrylate, dicyclopentanyl oxyethyl methacrylate,dicyclopentanyl oxyethyl acrylate, tricyclopentanyl methacrylate,tricyclopentanyl acrylate, 1-adamantyl methacrylate, 1-adamantylacrylate, 2-methyl-2-adamantyl methacrylate, 2-methyl-2-adamantylacrylate, 2-ethyl-2-adamantyl methacrylate, and 2-ethyl-2-adamantylacrylate. These (meth)acrylic monomers can be used alone or incombination of two or more thereof.

A functional group reactive with an epoxy group or an isocyanate groupmay be further introduced into the (meth)acrylic polymer (E). Examplesof such a functional group include a hydroxyl group, carboxyl group,amino group, amide group, and a mercapto group. When the (meth)acrylicpolymer (E) is produced, it is preferable to use a monomer having such afunctional group.

The weight average molecular weight (M_(WE)) of the (meth)acrylicpolymer (E) is 1000≦M_(WE)<30000, preferably 1500≦M_(WE)<20000, and morepreferably 2000≦M_(WE)<10000. If 30000≦M_(WE), the effect of improvingthe pressure-sensitive adhesive force of a pressure-sensitive adhesivetape may not be sufficiently obtained. Conversely, if M_(WE)<1000, themolecular weight is too small, and hence the pressure-sensitive adhesiveforce or holding property of a pressure-sensitive adhesive tape may bedecreased.

A weight average molecular weight can be determined by polystyreneconversion with the use of a GPC method. Specifically, a weight averagemolecular weight can be measured by using HPLC8020 made by TOSOHCORPORATION and two TSKgelGMH-H (20) columns, and under conditions inwhich a tetrahydrofuran solvent is used and a flow rate is approximately0.5 ml/min.

The content of the acrylic oligomer (E) is preferably within a range of2 to 70 parts by mass, and more preferably within a range of 5 to 50parts by mass, based on 100 parts by mass of the acrylic polymer (D). Ifthe (meth)acrylic polymer (E) is added in an amount more than 70 partsby mass, the elastic modulus of a pressure-sensitive adhesive layerformed of the acrylic pressure-sensitive adhesive composition accordingto the present embodiment becomes large, and hence the adhesiveness at alow-temperature may be deteriorated or the pressure-sensitive adhesiveforce may not be exerted even at room temperature. Conversely, if thecontent is less than 2 parts by mass, the effect of adding the(meth)acrylic polymer (E) may not be obtained.

The glass transition temperature (Tg) of the (meth)acrylic polymer (E)is approximately 20° C.≦Tg≦300° C., preferably approximately 30°C.≦Tg≦300° C., and more preferably approximately 40° C.≦Tg≦300° C. If Tgis lower than approximately 20° C., the cohesive force of apressure-sensitive adhesive layer is decreased at room temperature orhigher, and hence the holding property and the adhesiveness athigh-temperature may be decreased. In the present embodiment, the glasstransition temperatures of typical materials that can be used as the(meth)acrylic polymer (E) are shown in Table 1. The glass transitiontemperatures shown there are nominal values described in documents orcatalogs, etc., or values calculated based on the following Equation (3)(Fox Equation):

1/Tg=W1/Tg1+W2/Tg2+ . . . +Wn/Tgn  (3)

[wherein Tg represents the glass transition temperature (unit: K) of the(meth)acrylic polymer (E), Tgi (i=1, 2, . . . , n) represents the glasstransition temperature (unit: K) when monomer i forms a homopolymer, andWi (i=1, 2, . . . , n) represents a mass fraction of the monomer i inthe whole monomer components.] The above Equation (3) is adopted whenthe (meth)acrylic polymer (E) is formed of n types of monomer componentsof monomer 1, monomer 2, . . . , monomer n.

TABLE 1 COMPOSITION OF (METH) ACRYLIC Tg POLYMER (E) (° C.) REMARKSDCPMA 175 VALUES DESCRIBED IN DOCUMENTS, ETC. DCPA 120 VALUES DESCRIBEDIN DOCUMENTS, ETC. IBXMA 173 VALUES DESCRIBED IN DOCUMENTS, ETC. IBXA 97VALUES DESCRIBED IN DOCUMENTS, ETC. CHMA 66 VALUES DESCRIBED INDOCUMENTS, ETC. MMA 105 VALUES DESCRIBED IN DOCUMENTS, ETC. ADMA 250VALUES DESCRIBED IN DOCUMENTS, ETC. ADA 153 VALUES DESCRIBED INDOCUMENTS, ETC. DCPMA/IBXMA40 174 CALCULATED VALUES (BASED ON FoxEQUATION) DCPMA/MMA40 144 CALCULATED VALUES (BASED ON Fox EQUATION)DCPMA/MMA60 130 CALCULATED VALUES (BASED ON Fox EQUATION) IBXMA/MMA60130 CALCULATED VALUES (BASED ON Fox EQUATION) ADMA/MMA40 180 CALCULATEDVALUES (BASED ON Fox EQUATION) ADA/MMA40 132 CALCULATED VALUES (BASED ONFox EQUATION) CHMA/IBMA40 51 CALCULATED VALUES (BASED ON Fox EQUATION)

The abbreviations in Table 1 represent the following compounds.

DCPMA: Dicyclopentanyl Methacrylate

DCPA: Dicyclopentanyl Acrylate

IBXMA: Isobornyl Methacrylate

IBXA: Isobornyl Acrylate

CHMA: Cyclohexyl Methacrylate

MMA: Methyl Methacrylate

ADMA: 1-Adamantyl Methacrylate

ADA: 1-Adamantyl Acrylate

DCPMA/IBXMA 40: Copolymer of 60 parts by mass of DCPMA and 40 parts bymass of IBXMA

DCPMA/MMA 40: Copolymer of 60 parts by mass of DCPMA and 40 parts bymass of MMA

DCPMA/MMA 60: Copolymer of 40 parts by mass of DCPMA and 60 parts bymass of MMA

IBXMA/MMA 60: Copolymer of 40 parts by mass of IBXMA and 60 parts bymass of MMA

ADMA/MMA 40: Copolymer of 60 parts by mass of ADMA and 40 parts by massof MMA

ADA/MMA 40: Copolymer of 60 parts by mass of ADA and 40 parts by mass ofMMA

CHMA/IBMA 40: Copolymer of 60 parts by mass of CHMA and 40 parts by massof IBMA

<Method of Producing (Meth)Acrylic Polymer (E)>

The (meth)acrylic polymer (E) can be produced, for example, bypolymerizing the (meth)acrylic monomer having the aforementionedstructure with the use of a solution polymerization method, bulkpolymerization method, emulsion polymerization method, suspensionpolymerization method, block polymerization method, or the like.

<Method of Adjusting Molecular Weight of (Meth)Acrylic Polymer (E)>

In order to adjust the molecular weight of the (meth)acrylic polymer(E), a chain transfer agent can be used while the polymer (E) is beingpolymerized. Examples of the chain transfer agent to be used include:compounds having a mercapt group, such as octylmercaptan, t-nonylmercaptan, dodecyl mercaptan, t-dodecyl mercaptan, mercaptoethanol, andα-thioglycerol; thioglycolic acid, methyl thioglycolate, ethylthioglycolate, propyl thioglycolate, butyl thioglycolate, t-butylthioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctylthioglycolate, decyl thioglycolate, dodecyl thioglycolate, thioglycolicacid ester of ethylene glycol, thioglycolic acid ester of neopentylglycol, and thioglycolic acid ester of pentaerythritol. Examples of theparticularly preferred chain transfer agent, from the viewpoint of metalcorrosiveness, include α-thioglycerol, mercaptoethanol, methylthioglycolate, ethyl thioglycolate, propyl thioglycolate, butylthioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octylthioglycolat, and isooctyl thioglycolate.

The use amount of the chain transfer agent is not particularly limited,but the chain transfer agent is usually contained in an amount within arange of approximately 0.1 to approximately 20 parts by mass, preferablywithin a range of approximately 0.2 to approximately 15 parts by mass,and more preferably within a range of approximately 0.3 to approximately10 parts by mass, based on 100 parts by mass of the (meth)acrylicmonomer. By adjusting the use amount of the chain transfer agent, asstated above, the (meth)acrylic polymer (E) having a preferred molecularweight can be obtained. The chain transfer agents can be used alone orin combination of two or more thereof.

The weight average molecular weights of the acrylic polymers (A) and (D)and the (meth)acrylic polymer (E) can be determined by polystyreneconversion with the use of a GPC method. Specifically, the weightaverage molecular weights can be measured by using HPLC 8020 made byTOSOH CORPORATION and two TSKgelGMH-H (20) columns, and under conditionsin which a tetrahydrofuran solvent is used and a flow rate is 0.5ml/min.

(Thickness of Pressure-Sensitive Adhesive Layer)

In the present invention, the thickness of the pressure-sensitiveadhesive layer (when the core layer and the surface layer are present,the total thickness thereof) is 0.2 to 2.0 mm, and preferably 0.6 to 2.0mm.

(Layer Thickness Ratio)

The ratio of the thickness of the surface layer 18 a (or surface layer18 b) to the total thickness of both the thickness of the core layer 16and that of the surface layer 18 a (or surface layer 18 b) is preferablyapproximately 3 to approximately 70%. If the ratio is less thanapproximately 3%, desired adhesiveness may not be obtained. On the otherhand, if the ratio is more than 70%, the effects that can be expectedwhen a pressure-sensitive adhesive tape has the core layer 16 containingthe bubble (C), such as a stress relaxation property and leveldifference absorbing property, may not be obtained.

(Method of Forming Multi-Layers)

A method of laminating the core layer 16 and the surface layer 18 is notparticularly limited, but for example, the methods described below canbe applied.

(1) A method of forming multi-layers in which, after the core layer 16and the surface layer 18 are cured separately, the surface layer 18 a islaminated on one surface of the core layer 16 and the surface layer 18 bon the other surface of the core layer 16: this method has the advantagethat the accuracy of each layer thickness can be enhanced.

(2) A method in which, after the core layer 16 is coated on the surfacelayer 18 a (or surface layer 18 b) that has been cured beforehand, thecore layer 16 is cured, and subsequently the surface layer 18 b (orsurface layer 18 a) is coated on the core layer 16, and then the surfacelayer 18 b (or surface layer 18 a) is cured, or a method in which, afterthe surface layer 18 a is coated on one surface (or surface layer 18 bis coated on the other surface) of the core layer 16 that has been curedbeforehand, the surface layer 18 a (or surface layer 18 b) is cured, andsubsequently the surface layer 18 b is coated on the other surface (orsurface layer 18 a is coated on the one surface) of the core layer 16,and then the surface layer 18 b (or surface layer 18 a) is cured: inthis method, because one layer is coated on another layer that has beencured, the accuracy of each layer thickness can be enhanced. Further,because layers can be collectively coated on another layer that has beencured, production steps can be simplified and a production time can beshortened.

(3) A method in which, after the core layer 16 (or surface layer 18) issequentially or simultaneously coated on the coated surface layer 18 (orcore layer 16), they are cured: in this method, both the surface layer18 and the core layer 16 can be collectively coated.

For the formation of each layer, a coating roll, such as a roll coateror comma coater, may be used, or a slot die may be used. In particular,in the aforementioned method (3), a multi-layer slot die for coatingeach layer may also be used.

According to the aforementioned acrylic pressure-sensitive adhesivetape, the adhesive force to adherends having low polarity, such aspolystyrene, ABS, and polycarbonate, can be improved by including amultilayer structure in which the surface layer containing the acrylicpolymer and the (meth)acrylic polymer (E) and the core layer arelaminated each other.

In the acrylic pressure-sensitive adhesive tape of the aforementionedembodiment, the surface layers are provided on both the sides of thecore layer, but the surface layer may be provided on one side of thecore layer.

[Pressure-Sensitive Adhesive Tape]

The pressure-sensitive adhesive tape according to the present embodimentincludes: a pressure-sensitive adhesive layer (12 in FIG. 1) thatcontains a fine particle and/or a bubble and both the surfaces of whichare pressure-sensitive adhesive surfaces; and a release liner havingboth a release layer (a) (first release layer 28 in FIG. 3) that isprovided on one surface (1) (12 a in FIG. 1) of the pressure-sensitiveadhesive layer so as to contact the one surface (1) and a back surfacerelease layer (b) (second release layer 30 in FIG. 3) located oppositeto the release layer (a).

Because the pressure-sensitive adhesive tape according to the presentembodiment has the aforementioned structure, the following structure isformed when the pressure-sensitive adhesive tape is wound into a rollshape (or when a plurality of the sheet-shaped pressure-sensitiveadhesive tapes are laminated each other), in which the other surface ofthe pressure-sensitive adhesive layer contacts the back surface releaselayer (b) (second release layer 30 in FIG. 3) in a peelable manner.

In the pressure-sensitive adhesive tape according to the presentembodiment, a holding time during which the pressure-sensitive adhesivelayer and the back surface release layer (b) of the release liner areheld together, the holding time being measured according to thelater-described measuring method, is 2500 minutes or longer, preferably3000 minutes or longer, and most preferably 3300 minutes or longer. Bymaking the holding time 2500 minutes or longer, oozing of thepressure-sensitive adhesive (paste oozing) from the side surface can besuppressed in the pressure-sensitive adhesive tape wound into a rollshape.

In the present embodiment, it is particularly preferable that therelease liner has the following structure, in order to adjust theholding time to be within the aforementioned range:

(1) a structure in which the release liner has: a base layer containinga polyolefin resin; and a release layer (a) that contains low-densitypolyethylene and is provided on at least one side of the base layer soas to contact the pressure-sensitive adhesive layer; or

(2) a structure in which the release liner has: a base layer containinga polyolefin resin; a release layer (a) that contains linear low-densitypolyethylene and is provided on one side of the base layer so as tocontact the pressure-sensitive adhesive layer; and a back surfacerelease layer (b) that contains linear low-density polyethylene and isprovided on the other side of the base layer.

When the pressure-sensitive adhesive layer is formed to have amultilayer structure including: a core layer that contains the acrylicpolymer (A), the fine particle (B) and/or the bubble (C); and a surfacelayer that is provided on one or both sides of the core layer andcontains the acrylic polymer (D) and the (meth)acrylic polymer (E)having a weight average molecular weight (M_(WE)) of 1000≦M_(WE)<30000,oozing of the pressure-sensitive adhesive (paste oozing) from the sidesurface can be remarkably suppressed in the pressure-sensitive adhesivetape wound into a roll shape.

In the pressure-sensitive adhesive tape according to the presentembodiment, the peeling force, occurring when the release liner ispeeled from the pressure-sensitive adhesive layer in a 180°-peelingdirection, at a tensile speed of 300 mm/min, and in an environment of anambient temperature of 23° C., is 1.0 [N/25 mm] or more, and preferably1.2 [N/25 mm] or more (the upper limit is 5 [N/25 mm]). By making thepeeling force 1.0 [N/25 mm] or more, oozing of the pressure-sensitiveadhesive (paste oozing) from the side surface can be suppressed in thepressure-sensitive adhesive tape wound into a roll shape. Herein, thepeeling force refers to one between the pressure-sensitive adhesivelayer and the back surface release layer (b) of the release liner.

In a pressure-sensitive adhesive sheet with the release liner accordingto the present embodiment, pop-off or peeling of the release liner isnot caused even when stored in a curved state, and the sheet can exhibitan excellent peeling function when in use. Further, oozing of thepressure-sensitive adhesive from the pressure-sensitive adhesive tapewound into a roll shape can be suppressed. Accordingly, in thepressure-sensitive adhesive tape according to the present embodiment,blocking can be prevented from occurring in the state of being woundinto a roll shape, and hence the tape can be stored for a long period oftime in the state.

EXAMPLES

Hereinafter, the present embodiment will be described in more detailbased on Examples, but the present invention should not be limited atall by these Examples. In the following Examples, Comparative Example,and Table 2, the surface layer to be attached to a pressure-sensitiveadhesive tape is referred to as a “surface layer (pressure-sensitiveadhesive layer side)” and the surface layer located opposite thereto isreferred to as a “surface layer (back surface side)”.

Example 1 Release Liner

As the material of the surface layer (pressure-sensitive adhesive layerside), a low-density polyethylene resin (product name: “Novatec LDUF641” made by JAPAN POLYETHYLENE CORPORATION, density: 927 kg/m³) wasused. As the material of each of the base layer and the surface layer(back surface side), a mixed material (mixing mass ratio of thefollowing high-density polyethylene/low-density polyethylene: 60/40) wasused, in which the high-density polyethylene was a resin (product name:“HI-ZEX 3300F” made by Prime Polymer Co. Ltd., density: 950 kg/m³) andthe low-density polyethylene was a resin (product name: “Novatec LDLF440HB” made by JAPAN POLYETHYLENE CORPORATION, density: 925 kg/m³).

A release liner (thickness: 149 μm), formed by a three-layered structure(surface layer (pressure-sensitive adhesive layer side)/baselayer/surface layer (back surface side) (thickness: 21 μm/64 μm/64 μm),was produced by a three-layer co-extrusion T-die molding method, withthe use of a rubber textured roll as a touch roll on thepressure-sensitive adhesive sheet side and a metallic textured roll as atouch roll on the back surface side.

The surface roughness (Ra) (arithmetic mean roughness: Ra) of thesurface layer (pressure-sensitive adhesive layer side) provided on oneside of the obtained release liner was 0.10 μm, and that of the surfacelayer (back surface side) located opposite thereto was 0.20 μm.

(Pressure-Sensitive Adhesive Layer)

Core Layer

After a photo-polymerization initiator (product name: “IRGACURE 651”made by Ciba Specialty Chemicals Corp., 0.05 parts by mass) and aphoto-polymerization initiator (product name: “IRGACURE 184” made byCiba Specialty Chemicals Corp., 0.05 parts by mass) were blended in amonomer mixture formed by 2-ethylhexyl acrylate (90 parts by mass) andan acrylic acid (10 parts by mass), the mixture was irradiated withultraviolet rays before the viscosity thereof (BH viscometer, No. 5rotor, 10 rpm, measurement temperature: 30° C.) became 15 Pa·s, therebyallowing a composition (acrylic polymer syrup 1) in which part of themonomer components were polymerized to be obtained.

After 1,6-hexanediol diacrylate (0.08 parts by mass) and aphoto-polymerization initiator (product name: “IRGACURE 651” made byCiba Specialty Chemicals Corp., 0.04 parts by mass) were added to theacrylic polymer syrup 1 (100 parts by mass), a hollow glass microsphere(product name: “CEL-STAR Z-27” made by Tokai Kogyo Co., Ltd.) was addedin an amount of 9.5 parts by mass based on the partially polymerizedmonomer syrup.

A precursor of a pressure-sensitive adhesive composition was prepared byadding a fluorochemical surfactant (product name: Surflon S-393 made byAGC SEIMI CHEMICAL CO., LTD.; an acrylic copolymer having apolyoxyethylene group and a fluorinated hydrocarbon group in its sidechain; M_(w)=8300, 0.5 parts by mass) to the acrylic polymer syrup 1 towhich the hollow glass microsphere had been added. In the precursor of apressure-sensitive adhesive composition, the ratio of the volume of thehollow glass microsphere to the whole volume of the precursor thereofwas approximately 23% by volume.

An acrylic pressure-sensitive adhesive composition 1 for the core layerwas obtained by introducing the precursor of a pressure-sensitiveadhesive composition between the teeth on a stator and the teeth on arotor in an apparatus (which is provided with: the stator having manyfine teeth on a disc with a through-hole at its center; and a rotorhaving teeth they are as fine as those on the stator and provided on adisc, the rotor facing the stator) and then by introducing nitrogen gasinto the precursor thereof via the through-hole while rotating the rotorat high-speed, that is, by mixing bubbles into the precursor thereof.The bubbles were mixed such that the content thereof was approximately20% by volume, based on the whole volume of the acrylicpressure-sensitive adhesive composition 1.

The acrylic pressure-sensitive adhesive composition 1 was applied on asurface of a polyester film (release liner made of polyester, onesurface of which has been subjected to a peeling treatment, thickness:38 μm), the surface being the peeling-treated surface, with a rollcoater so as to have a thickness of 550 μm. Subsequently, a polyesterrelease liner of the same type was attached to the other surface of theapplied acrylic pressure-sensitive adhesive composition 1 such that thepeeling-treated surface of the polyester release liner faced the othersurface of the acrylic pressure-sensitive adhesive composition 1.Subsequently, both the sides of the aforementioned object wereirradiated with UV rays by using a black light lamp having anilluminance of 5 mW/cm². Thus, a core layer formed by an acrylicpressure-sensitive adhesive layer having a thickness of 550 μm wasobtained.

Surface Layer

After a photo-polymerization initiator (product name: “IRGACURE 651”made by Ciba Specialty Chemicals Corp., 0.07 parts by mass) and aphoto-polymerization initiator (product name: “IRGACURE 184” made byCiba Specialty Chemicals Corp., 0.07 parts by mass) were blended in amonomer mixture formed by 2-ethylhexyl acrylate (94 parts by mass) andan acrylic acid (6 parts by mass), the mixture was irradiated with UVrays before the viscosity thereof (BH viscometer, No. 5 rotor, 10 rpm,measurement temperature: 30° C.) became 15 Pa·s, thereby allowing apartially polymerized composition (acrylic polymer syrup 2) to beobtained.

After cyclohexyl methacrylate (CHMA, 60 parts by mass), isobutylmethacrylate (IBMA, 40 parts by mass), and thioglycolic acid (4.0 partsby mass) were blended, dissolved oxygen was removed by blowing nitrogengas thereinto. After the mixture was heated to 90° C., PERHEXYL O (madeby NOF CORPORATION, 0.005 parts by mass) and PERHEXYL D (made by NOFCORPORATION, 0.01 parts by mass) were mixed. After being further stirredat 90° C. for 1 hour, the mixture was heated to 150° C. in 1 hour andstirred at the temperature for 1 hour. Subsequently, the mixture washeated to 170° C. in 1 hour and stirred at the temperature for 60minutes.

The pressure under which the mixture was put was reduced at 170° C. andthe mixture was stirred for 1 hour to remove remaining monomers, therebyallowing the (meth)acrylic polymer (E) to be obtained. The weightaverage molecular weight of the obtained (meth)acrylic polymer (E) was3700.

An acrylic pressure-sensitive adhesive composition 2 for surface layerwas obtained by blending 2-isocyanatoethyl acrylate (0.08 parts by mass)and the (meth)acrylic polymer (E) thus obtained (20 parts by mass) inthe aforementioned acrylic polymer syrup 2 (100 parts by mass).

The acrylic pressure-sensitive adhesive composition 2 was applied to asurface of a polyester film (release liner made of polyester, onesurface of which has been subjected to a peeling treatment, thickness:38 μm), the surface being the peeling-treated surface, with a rollcoater so as to have a thickness of 50 μm. Subsequently, a polyesterrelease liner of the same type was attached to the other surface of theapplied acrylic pressure-sensitive adhesive composition 2 such that thepeeling-treated surface of the polyester release liner faced the othersurface of the acrylic pressure-sensitive adhesive composition 2.Subsequently, both the sides of the aforementioned object wereirradiated with UV rays by using a black light lamp having anilluminance of 5 mW/cm². Thus, a surface layer formed by an acrylicpressure-sensitive adhesive layer having a thickness of 50 μm wasobtained.

(Attachment of Surface Layer/Core Layer/Surface Layer)

A pressure-sensitive adhesive layer (having a three-layered structure(surface layer (50 μm)/core layer (550 μm)/surface layer (50 μm)) wasproduced by attaching the surface layers to both the surfaces of thecore layer, the surface layers and the core layer being obtained in theabove procedures. Herein, the core layer was a pressure-sensitiveadhesive layer containing bubbles and fine particles.

A pressure-sensitive adhesive tape was produced by attaching thepressure-sensitive adhesive layer to the surface of the surface layer(pressure-sensitive adhesive layer side) of the aforementioned releaseliner and then by winding it into a roll shape.

Example 2 Release Liner

As the material of each of the surface layers (pressure-sensitiveadhesive layer side, back surface side), a mixed material was used, themixed material being made by 100 parts by mass of a linear low-densitypolyethylene resin (product name “MORETEC 0628D” made by Prime PolymerCo. Ltd., density: 916 kg/m³) and 15 parts by mass of anethylene-propylene copolymerized elastomer (product name: “TAFMER P0280”made by Mitsui Chemicals, Inc., density: 870 kg/m³). As the material ofthe base layer, 100 parts by mass of a polypropylene resin (productname: “Noblen FS3611” made by Sumitomo Chemical Co., Ltd., density: 890kg/m³) were used.

A release liner (thickness: 150 μm), formed by a three-layered structure(surface layer (pressure-sensitive adhesive layer side)/baselayer/surface layer (back surface side) (thickness: 8 μm/134 μm/8 μm),was produced by a three-layer co-extrusion T-die molding method, withthe use of a rubber textured roll as a touch roll on thepressure-sensitive adhesive sheet side and a metallic textured roll as atouch roll on the back surface side.

The surface roughness (Ra) (arithmetic mean roughness: Ra) of thesurface layer (pressure-sensitive adhesive layer side) on one side ofthe obtained release liner was 0.10 μm, and that of the surface layer(back surface side) located opposite thereto was 0.65 μm.

(Pressure-Sensitive Adhesive Layer)

A pressure-sensitive adhesive tape was produced by attaching apressure-sensitive adhesive layer, the same as that in Example 1, to thesurface layer (pressure-sensitive adhesive layer side) on one side ofthe aforementioned release liner and then by winding it into a rollshape.

Comparative Example 1 Release Liner

As the material of each of the surface layers (pressure-sensitiveadhesive layer side, back surface side), a mixed material was used, themixed material being made by 100 parts by mass of a linear low-densitypolyethylene resin (product name “MORETEC 0628D” made by Prime PolymerCo. Ltd., density: 916 kg/m³) and 50 parts by mass of anethylene-propylene copolymerized elastomer (product name: “TAFMER P0280”made by Mitsui Chemicals, Inc., density: 870 kg/m³). As the material ofthe base layer, 100 parts by mass of a polypropylene resin (productname: “Noblen FS3611” made by Sumitomo Chemical Co., Ltd., density: 890kg/m³) were used.

A release liner (thickness: 150 μm), formed by a three-layered structure(surface layer (pressure-sensitive adhesive sheet side)/baselayer/surface layer (back surface side) (thickness: 8 μm/134 μm/8 μm),was produced by a three-layer co-extrusion T-die molding method, withthe use of a rubber textured roll as a touch roll on thepressure-sensitive adhesive sheet side and a metallic textured roll as atouch roll on the back surface side.

The surface roughness (Ra) (arithmetic mean roughness: Ra) of thesurface layer (pressure-sensitive adhesive layer side) on one side ofthe obtained release liner was 0.82 μm, and that of the surface layer(back surface side) located opposite thereto was 1.35 μm.

(Pressure-Sensitive Adhesive Layer)

A pressure-sensitive adhesive tape was produced by attaching apressure-sensitive adhesive layer, the same as that in Example 1, to thesurface layer (pressure-sensitive adhesive layer side) of theaforementioned release liner and then by winding it into a roll shape.

The properties of the pressure-sensitive adhesive tapes according toExample 1, Example 2, and Comparative Example 1, which were produced asdescribed above, are shown in Table 2.

TABLE 2 COMPARATIVE EXAMPLE 1 EXAMPLE 2 EXAMPLE 1 RELEASE SURFACE LAYEROLEFIN RESIN LDPE1 LLDPE1 LLDPE1 LINER (PRESSURE-SENSITIVE ELASTOMER —ADDITION ADDITION ADHESIVE COMPOUNDING RATIO 100/0 100/15 100/50 LAYERSIDE) (RESIN/ELASTOMER) BASE LAYER RESIN HDPE/LDPE2 PP PP SURFACE LAYEROLEFIN RESIN HDPE/LDPE2 LLDPE1 LLDPE1 (BACK SURFACE ELASTOMER — ADDITIONADDITION SIDE) COMPOUNDING RATIO 100/0 100/15 100/50 (RESIN/ELASTOMER)LAYER SURFACE LAYER 21 8 8 THICKNESS (μm) (PRESSURE-SENSITIVE ADHESIVELAYER SIDE) BASE LAYER 64 134 134 SURFACE LAYER 64 8 8 (BACK SURFACESIDE) TOTAL THICKNESS (μm) 149 150 150 PRESSURE- PRESSURE-SENSITIVEACRYLIC ACRYLIC ACRYLIC SENSITIVE ADHESIVE COMPOSITION ADHESIVE BUBBLESTRUCTURE BUBBLE BUBBLE BUBBLE LAYER EVALUATION PASTE PROTRUSION ∘ ∘ xRESULTS PROPERTY CREEP TEST HOLDING TIME [min] 3790 3373 2432PEELABILITY PEELING FORCE [N/25 mm] 2.53 1.3 0.79

The pressure-sensitive adhesive tapes according to Example 1, Example 2,and Comparative Example 1 were evaluated in accordance with thefollowing evaluation methods. Results of the evaluation are also shownin Table 2.

[Method of Measuring Physical Properties and Method of EvaluatingEffects] (1) Evaluation of Paste Oozing Property

Presence/absence of paste oozing from the side surface of thepressure-sensitive adhesive tape (sample), obtained in each of Examplesand Comparative Example, was confirmed in the following way: the sampletape (size: 25 mm in width×20 m in wound length, wound into a rollshape) was left uncontrolled in an atmosphere of 50° C. for one week;and then, after being left uncontrolled in an atmosphere of 23° C.×50%RH for one day, the sample tape was observed. The tape in which no pasteoozing was observed was evaluated as O, while the tape in which pasteoozing was observed was evaluated as x.

In the pressure-sensitive adhesive tape according to each of Examples 1and 2, no paste oozing was observed. On the other hand, in thepressure-sensitive adhesive tape according to Comparative Example 1,paste oozing was observed.

Additionally, as a result of intensive study of the evaluation of pasteoozing, the present inventors have conceived of the possibility that apaste oozing property can be indirectly evaluated by measuring one ofthe states associated with paste oozing, other than direct methods suchas the aforementioned visual observation.

One of the states is a holding time in a creep test performed in a statewhere the back surface release layer (b) (second release layer 30 inFIG. 3) of the release liner and the other surface of thepressure-sensitive adhesive layer 12 of the acrylic pressure-sensitiveadhesive tape 10 are pressure-bonded. Another of the states is amagnitude of the peeling force between the back surface release layer(b) (second release layer 30 in FIG. 3) of the release liner and theother surface of the pressure-sensitive adhesive layer 12 of the acrylicpressure-sensitive adhesive tape 10. Hereinafter, two evaluation methodswill be described in detail.

(2) Holding Time in Creep Test

It can be considered that one reason for paste oozing is that the othersurface of the pressure-sensitive adhesive layer is shifted little bylittle from the back surface release layer (b) of the release liner in astate where the pressure-sensitive adhesive tape is wound into a rollshape. Accordingly, when the pressure-sensitive adhesive force betweenthe pressure-sensitive adhesive layer and the back surface release layerof the separator is large, a slippage is hardly caused and paste oozingcan be prevented from occurring.

A measuring method in a creep test will be described with reference toFIGS. 4 to 7. Each element of the pressure-sensitive adhesive layer 12and the release liner 14 included in the acrylic pressure-sensitiveadhesive tape 10 will be denoted with the same reference numeral as thatin FIGS. 1 to 3, and description thereof will be appropriately omitted.The dimensions and size ratios of each element are conveniently set formaking the description and illustration thereof easy to understand, andthey should not be construed to be limitative.

FIG. 4( a) is a top view of a provided bakelite plate 32, and FIG. 4( b)is a side view of the bakelite plate 32 illustrated in FIG. 4( a). Thesize of the bakelite plates 32 illustrated in FIG. 4( a) is 25 mm×130mm. After the surface of the bakelite plate 32 is cleaned with IPA(isopropyl alcohol) and sufficiently dried, a double-sidedpressure-sensitive adhesive tape 34 (product name: No. 5000NS made byNITTO DENKO CORPORATION, size: 25 mm×100 mm) is attached to the cleanedsurface.

FIG. 5( a) is a top view of a state where the release liner 14 to bemeasured is attached to the bakelite plate 32 by using the double-sidedpressure-sensitive adhesive tape 34, and FIG. 5( b) is a side view ofthe state in FIG. 5( a).

The pressure-sensitive adhesive surface is exposed by peeling therelease liner attached to the double-sided pressure-sensitive adhesivetape 34, and then the first release layer 28 (release layer (a)) of therelease liner 14 to be measured (release liner of each of Examples andComparative Example) is attached to the double-sided pressure-sensitiveadhesive tape, thereby allowing the release liner 14 to be fixed to thebakelite plate 32. That is, the release liner 14 is fixed to thebakelite plate 32, with the second release layer 30 (back surfacerelease layer (b)) oriented upward.

FIG. 6( a) is a top view of a state where the acrylic pressure-sensitiveadhesive tape 10 is attached to the second release layer 30 (backsurface release layer (b)) of the release liner 14, and FIG. 6( b) is aside view of the state in FIG. 6( a).

The surface of the second release layer 30 (back surface release layer(b)) of the release liner 14 is cleaned with IPA. The acrylicpressure-sensitive adhesive tape 10 (with release liner) to be measuredis cut into a size of 25 mm×100 mm.

A test piece 36 is produced by attaching the other surface (surface onthe side not contacting the release liner) of the pressure-sensitiveadhesive layer of the acrylic pressure-sensitive adhesive tape 10 thuscut to the second release layer 30 (back surface release layer (b)) ofthe release liner 14 such that the contact area becomes 25 mm inwidth×40 mm in length.

In this state, the test piece 36 was pressure-bonded from the uppersurface of the acrylic pressure-sensitive adhesive tape 10 by moving a5-kg roller one way, and it was left still in an atmosphere of roomtemperature (23° C., 50% RH) for 24 hours. Thereafter, the test piece 36was left still in an atmosphere of 40° C. for 30 minutes.

FIG. 7 is a view illustrating a situation where the test piece issubjected to a creep test. As illustrated in FIG. 7, the test piece 36was hung to a fixed part 38 such that the bakelite plate 32 is locatedupward and the acrylic pressure-sensitive adhesive tape 10 locateddownward, and a weight 40 was hung to the lower end of the acrylicpressure-sensitive adhesive tape 10. The weight 40 was 200 g. That is, aholding time, until the acrylic pressure-sensitive adhesive tape 10drops off from the test piece 36, is measured by applying a load of 1.96N (0.2 kgf) to the lower end portion of the pressure-sensitive adhesivetape 10, the lower end portion not contacting the test piece, in thelongitudinal direction of the pressure-sensitive adhesive tape, and inan environment of an ambient temperature of 40° C. In the test pieceusing the pressure-sensitive adhesive tape according to Example 1,drop-off of the tape was not observed even after 63 hours passed.Results of measuring the holding times of the tapes according to Example1, Example 2, and Comparative Example 1 are shown in Table 2.

As shown in Table 2, the holding time of the pressure-sensitive adhesivetape according to each of Examples 1 and 2 is 2500 minutes or longer. Onthe other hand, the holding time of the pressure-sensitive adhesive tapeaccording to Comparative Example 1 is shorter than 2500 minutes. Thus,the back surface release layer (b) (second release layer 30) of therelease liner is structured such that a holding time, occurring whenmeasured by the aforementioned creep test, is 2500 minutes or longer. Itis more preferable that the back surface release layer of the releaseliner is structured such that the holding time is 3000 minutes orlonger. In a pressure-sensitive adhesive tape including a release linerhaving such a structure, oozing of the pressure-sensitive adhesive issuppressed. In a tape roll in which such a pressure-sensitive adhesivetape is wound into a roll shape, oozing of the pressure-sensitiveadhesive is suppressed even in the state of being wound into the rollshape.

(3) Magnitude of Peeling Force Between Back Surface Release Layer (b)(Second Release Layer 30 in FIG. 3) of Release Liner and Other Surfaceof Pressure-Sensitive Adhesive Layer 12 of Acrylic Pressure-SensitiveAdhesive Tape 10.

It can be considered that, in a pressure-sensitive adhesive tape inwhich larger force is required for peeling a release liner, oozing ofthe pressure-sensitive adhesive layer 12 from the release liner 14 ismore hardly caused in the state of being wound into a roll shape. So,the peeling force between the back surface release layer (b) (secondrelease layer 30 in FIG. 3) of the release liner and the other surfaceof the pressure-sensitive adhesive layer 12 of the acrylicpressure-sensitive adhesive tape 10 was measured by a peeling test.

An evaluation sample (size: 25 mm in width×150 mm in length), in a statewhere a release liner/a pressure-sensitive adhesive layer/a releaseliner/a pressure-sensitive adhesive layer are laminated each other(i.e., in a state where two pressure-sensitive adhesive tapes arelaminated one on another), was first cut out from the pressure-sensitiveadhesive tape obtained in each of Examples and Comparative Example. Theexposed pressure-sensitive adhesive layer (pressure-sensitive adhesivelayer of the pressure-sensitive adhesive tape located downward) wasattached to a supporting plate (SUS 304 BA plate, 50 mm×150 mm). Herein,the longitudinal direction of the sample is the direction in which thepressure-sensitive adhesive sheet flows.

Peeling force, occurring when the pressure-sensitive adhesive tape(release liner/pressure-sensitive adhesive layer) located upward waspeeled from the back surface release layer (b) of the release liner ofthe pressure-sensitive adhesive tape located downward, in a 180°-peelingdirection by using a universal testing machine (“TG-1kNB” made byMinebea Co., Ltd.), was measured. A maximum of peeling forces wasdetermined as the peeling force, the maximum being determined asfollows: peeling forces were measured by pulling the release liners; andthe top 10% and bottom 10% of the measured peeling forces were cut, andthe maximum of the remaining 80% thereof was determined as the abovemaximum.

In the pressure-sensitive adhesive tape according to each of Examples 1and 2, the peeling force was 1.0 [N/25 mm] or more. In thepressure-sensitive adhesive tape according to each of Examples 1 and 2that satisfy such conditions, no paste oozing was observed. On the otherhand, in the pressure-sensitive adhesive tape according to ComparativeExample 1, the peeling force, occurring when peeled in a 180°-peelingdirection and at a tensile speed of 300 mm/min, was less than 1.0 [N/25mm], and paste oozing was observed.

The present invention has been described above based on the embodimentsand examples. The embodiments and examples are described for exemplarypurposes only, and it can be readily understood by those skilled in theart that various modifications may be made by making variouscombinations of the aforementioned components or processes, which arealso encompassed in the scope of the present invention.

The present invention can be used for a pressure-sensitive adhesivetape. The invention can be particularly used for a tape roll(double-sided pressure-sensitive adhesive tape wound body) in which apressure-sensitive adhesive layer, both the surfaces of which arepressure-sensitive adhesive surfaces, and a release liner laminated onthe pressure-sensitive adhesive layer are wound into a roll shape.

1. A pressure-sensitive adhesive tape comprising: a pressure-sensitiveadhesive layer that contains at least a fine particle and/or a bubbleand both the surfaces of which are pressure-sensitive adhesive surfaces;and a release liner having both a release layer (a) that is provided onone surface (1) of the pressure-sensitive adhesive layer so as tocontact the one surface (1) and a back surface release layer (b) locatedopposite to the release layer (a), wherein a thickness of thepressure-sensitive adhesive layer is 0.2 to 2.0 mm, and wherein the backsurface release layer (b) of the release liner is structured such that aholding time, measured in the following way (i) to (iv), is 2500 minutesor longer: (i) a test piece (size: 25 mm in width×100 mm in length),having the same material as that of the release liner, is provided so asto be fixed to a bakelite plate with the back surface release layer (b)oriented upward; (ii) the pressure-sensitive adhesive tape (size: 25 mmin width×100 mm in length) is provided, and the other surface (2) of thepressure-sensitive adhesive layer is attached to the back surfacerelease layer (b) of the test piece such that a contact area becomes 25mm in width×40 mm in length; (iii) the pressure-sensitive adhesive tapeis pressure-bonded by moving a 5-kg roller one way; and (iv) a holdingtime, until the pressure-sensitive adhesive tape drops off from the testpiece, is measured by applying a load of 1.96 N (0.2 kgf) to an endportion of the pressure-sensitive adhesive tape, the end portion notcontacting the test piece, in a longitudinal direction of thepressure-sensitive adhesive tape and in an environment of an ambienttemperature of 40° C.
 2. The pressure-sensitive adhesive tape accordingto claim 1, wherein peeling force, occurring when the release liner ispeeled from the pressure-sensitive adhesive layer in a 180°-peelingdirection, at a tensile speed of 300 mm/min, and in an environment of anambient temperature of 23° C., is 1.0 [N/25 mm] or more.
 3. Thepressure-sensitive adhesive tape according to claim 1, wherein therelease liner includes: a base layer containing a polyolefin resin; anda release layer (a) that contains low density polyethylene and isprovided on at least one side of the base layer so as to contact thepressure-sensitive adhesive layer.
 4. The pressure-sensitive adhesivetape according to claim 1, wherein the release liner includes: a baselayer containing a polyolefin resin; a release layer (a) that containslinear low-density polyethylene and is provided on one side of the baselayer so as to contact the pressure-sensitive adhesive layer; and a backsurface release layer (b) that contains linear low-density polyethyleneand is provided on the other side of the base layer.
 5. Thepressure-sensitive adhesive tape according to claim 1, wherein thepressure-sensitive adhesive layer includes: a core layer containing anacrylic polymer (A), a fine particle (B) and/or a bubble (C); and asurface layer that is provided on one or both sides of the core layerand contains an acrylic polymer (D) and a (meth)acrylic polymer (E)having a weight average molecular weight (M_(WE)) of 1000≦M_(WE)<30000.6. The pressure-sensitive adhesive tape according to claim 5, wherein acontent of the (meth)acrylic polymer (E) is 5 to 45 parts by mass, basedon 100 parts by mass of the acrylic polymer (D).
 7. Thepressure-sensitive adhesive tape according to claim 5, wherein each ofthe acrylic polymer (A) and the acrylic polymer (D) contains a(meth)acrylic acid alkyl ester as a monomer major component.
 8. Thepressure-sensitive adhesive tape according to claim 2, wherein therelease liner includes: a base layer containing a polyolefin resin; anda release layer (a) that contains low density polyethylene and isprovided on at least one side of the base layer so as to contact thepressure-sensitive adhesive layer.
 9. The pressure-sensitive adhesivetape according to claim 2, wherein the release liner includes: a baselayer containing a polyolefin resin; a release layer (a) that containslinear low-density polyethylene and is provided on one side of the baselayer so as to contact the pressure-sensitive adhesive layer; and a backsurface release layer (b) that contains linear low-density polyethyleneand is provided on the other side of the base layer.
 10. Thepressure-sensitive adhesive tape according to claim 2, wherein thepressure-sensitive adhesive layer includes: a core layer containing anacrylic polymer (A), a fine particle (B) and/or a bubble (C); and asurface layer that is provided on one or both sides of the core layerand contains an acrylic polymer (D) and a (meth)acrylic polymer (E)having a weight average molecular weight (M_(WE)) of 1000≦M_(WE)<30000.11. The pressure-sensitive adhesive tape according to claim 3, whereinthe pressure-sensitive adhesive layer includes: a core layer containingan acrylic polymer (A), a fine particle (B) and/or a bubble (C); and asurface layer that is provided on one or both sides of the core layerand contains an acrylic polymer (D) and a (meth)acrylic polymer (E)having a weight average molecular weight (M_(WE)) of 1000≦M_(WE)<30000.12. The pressure-sensitive adhesive tape according to claim 4, whereinthe pressure-sensitive adhesive layer includes: a core layer containingan acrylic polymer (A), a fine particle (B) and/or a bubble (C); and asurface layer that is provided on one or both sides of the core layerand contains an acrylic polymer (D) and a (meth)acrylic polymer (E)having a weight average molecular weight (M_(WE)) of 1000≦M_(WE)<30000.13. The pressure-sensitive adhesive tape according to claim 6, whereineach of the acrylic polymer (A) and the acrylic polymer (D) contains a(meth)acrylic acid alkyl ester as a monomer major component.
 14. A taperoll in which the pressure-sensitive adhesive tape according to any oneof claim 1 is wound into a roll shape.
 15. The pressure-sensitiveadhesive tape according to claim 6, wherein each of the acrylic polymer(A) and the acrylic polymer (D) contains a (meth)acrylic acid alkylester as a monomer major component.